the structure of reactive grain boundaries under stress containing confined fluids we present numerical experiments on structure development in grain boundaries during dissolution precipitation creep two solids that are represented by an elastic spring configuration are pressed together with a compressible fluid in the grain boundary the solid can dissolve or precipitate depending on elastic and surface energy as well as fluid pressure and concentration of dissolved material in the fluid we perform a number of numerical experiments with different starting configurations that represent a large scale island channel interface with solid solid contacts across the islands a rough grain boundary interface with a fluid along the whole interface and a smooth thin film interface the simulations suggest that the solid solid islands become unstable by necking and anti cracking so that the island channel interface will develop into a grain boundary interface the rough interface of the grain boundary will coarsen with time so that in the extreme case a smooth thin film interface will emerge however the thin film interface is also not necessarily stable but may develop into a rough grain boundary where the roughness is initiated by heterogeneous dissolution of the solid our numerical experiments suggest that interface structures during dissolution precipitation creep are transient and that the dominance of one interface structure depends on material properties the displacement rate purity of the reacting solid and the scale of observation

a pressure solution creep law for quartz from indentation experiments 1 indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions this deformation mechanism contributes to earth s crust geodynamics controlling processes as different as fault permeability strength and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism indenter experiments have been performed at 350 c and 20 120 mpa during months with differential stress varying from 25 to 350 mpa several experimental parameters were varied nature of quartz synthetic or natural nature of fluid manner in which the solid solution solid interface was filled and orientation of the indented surfaces versus quartz crystallographic c axis significant strain rates could only be obtained when using high solubility solutions naoh 1 mol l 1 displacement rates of the indenter were found activated by differential stress with exponential dependence as theoretically predicted the mean thickness of the trapped fluid phase below the indenter was estimated in the range 2 10 nm moreover the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution the indenter displacement rate was driven by differential stress and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface conversely marginal strain energy driven dissolution was observed around the indenter and its kinetics was controlled by free surface reaction these experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones providing characteristic time scales for postseismic transitory creep and sealing processes in quartz rich rocks

accelerated hydration of the earth s deep crust induced by stress perturbations the metamorphic cycle associated with the formation of mountain belts produces a lower crust containing little or no free fluid1 2 the introduction of external fluids to dry and impermeable volumes of the earth s crust is thus a prerequisite for the retrogressive metamorphism later observed in such regimes such metamorphism can cause significant changes in the crust s physical properties including its density rheology and elastic properties3 4 on a large scale the introduction of fluids requires the presence of high permeability channels such as faults or fractures which are the result of external tectonic stresses but extensive interaction between externally derived fluids and the fractured rock requires efficient mass transport away from the initial fractures into the rock itself and this transport often occurs over distances much longer than expected from grain boundary diffusion here we present both field observations and a simple network model that demonstrate how the transport of fluids into initially dry rock can be accelerated by perturbations in the local stress field caused by reactions with fluids we also show that the morphology of reaction fronts separating dry from wet rocks depends on the anisotropy of the external stress field

experimental compaction of quartz sand at low effective stress and temperature conditions experiments have been carried out on dry and fluid saturated quartz sands to investigate the behaviour during compaction under diagenetic conditions and to evaluate the importance of stress induced solution transfer 9pressure solution9 as a compaction mechanism the experiments were performed at temperatures t in the range 150 350 c applied effective stresses e up to 20 7 mpa and pore fluid pressures p 1 of 12 5 and 15 5 mpa using material with a grain size d in the range 20 100 m and an initial porosity of 45 52 dry quartz sands underwent significant compac tion during the loading stage but showed very little compaction creep once full load was achieved i e essentially time independent compaction in contrast fluid saturated material at constant applied effective stress showed substantial time dependent compaction i e creep with increasing temperature there is a decreasing number of grains in the wet compacted sand which show intragranular cracks and an increasing number of grains which show dissolution features at contacts with adjacent grains in addition there is a decreasing dependence of the volumetric strain rate on e with both increasing volumetric strain e v and increasing e and a decreasing dependence of on e v with increasing temperature these observations suggest that for wet quartz sand a gradual change might occur from compaction creep controlled by time dependent microcracking at t 250 300 c to compaction creep controlled by stress induced intergranular solution transfer at t 300 350 c

an s coordinate density evolving model of the northwest european continental shelf 1 model description and density structure the proudman oceanographic laboratory three dimensional baroclinic b grid model pol3db has been developed to incorporate features suitable for the modeling of baroclinic processes on the shelf at the shelf slope and in ocean regions to allow long term coupled ocean shelf simulations we test the model on the northwest european continental shelf in the period november 1988 to october 1989 against satellite sea surface temperature measurements against ctd sections both on and off the shelf and in summary against the whole of the north sea project ctd data set the model accurately reproduces the seasonal cycle in the shelf wide spatial temperature structure seen in the observations spatial correlations range from r 0 92 in december to 0 79 in july and the overall rms errors range from 0 8 c in april to 1 6 c in july we demonstrate that the increase in the errors during the summer is due to uncertainties in modeling the vertical temperature structure compared with a climatology the large scale sea surface salinity structure is also well modeled r 0 80 but there is a tendency for the model to overestimate the salinity in the norwegian trench and underestimate it in the kattegat the s coordinates a modified sigma coordinate system allow the formation of a seasonal mixed layer across the shelf break and into the northeast atlantic with a modest vertical resolution the accuracy to which this deep water region is modeled is limited by the initial and boundary conditions and by the extent of the model domain

geochemistry of ostracode calcite part 2 the effects of water chemistry and seasonal temperature variation on candona rawsoni abstract reconstruction of lake paleochemistry from the isotope and trace element composition of fossil ostracodes requires an understanding of geochemical variations induced by the seasonality of shell formation monthly field collections of live candona rawsoni from two hyposaline lakes in the eastern dakotas reveal large variations in 18 o values 2 5 o and mg ca and sr ca ratios up to 35 among individual adults within the same assemblage because the measured variations in water chemistry were small the amplitude of ostracode 18 o and mg ca variations must result from seasonal temperature variation ostracode sr ca ratios which should be temperature independent shows strong positive covariance with shell mg ca these results imply that sr uptake in ostracode calcite increases with the mg content of the shell the partitioning coefficient for mg on the other hand appears to decreases at high values of mg ca in the host water the geochemical variability in the field collections indicates that c rawsoni populations are composed of multiple overlapping generations that attain maturity at different times many juveniles apparently undergo several molts in mid summer and persist as penultimate instars a 1 into the following spring geochemical analysis of late instar juvenile c rawsoni from lacustrine sedimentary records is likely to provide information on mid summer conditions large numbers of fossil ostracodes should be analyzed from each stratigraphic interval to eliminate seasonal noise from the paleochemistry records of temperate region lakes

equilibrium partial pressure of co 2 in callovian oxfordian argillite as a func tion of relative humidity experiments and modelling having previously demonstrated that the mineral assemblage of claystone can impose its pco2 under saturated conditions we here study the effect of rock desaturation i e the evaporation of pore water on the partial pressure of co2 pco2 in callovian oxfordian argillite from the paris basin france in this new study which combines experiments at room temperature and geochemical modelling we examine the primary role of capillary forces on chemical equilibria for relative humidity values ranging between 50 and 100 in particular we are able without any fitting parameters to model the experimental decrease of pco2 as a function of decreasing water content in the argillite this application to a complex natural system not only confirms the theoretical concepts of geochemistry in capillary contexts but is promising with respect to other systems both natural soil rock and industrial ceramics granular material

calibration of past water temperature in the sea of japan based on mg ca of ostracode shells of two shallow marine species in the genus cytheropteron abstract compared to mg ca temperature calibrations in deep sea ostracodes and the use of these calibrations to understand past conditions there have been few studies of shallow marine ostracode taxa in the present study mg ca temperature calibrations were constructed for two shallow marine ostracode species belonging to the genus cytheropteron in the recent sediments of the sea of japan in order to reconstruct the past water temperature record in shallow sea areas the mg ca of adult cytheropteron miurense and cytheropteron sawanense shells from nine bottom sediment samples was positively correlated with the mean annual water temperature wt according to the following equation wt c mg ca of ostracode shell mmol mol 0 94 9 53 comparison of the regression curves of mg ca versus wt for six genera showed similar temperature sensitivity of mg uptake in shells of cytheropteron sarsicytheridea and the genus krithe in most cases but lower than those for genera bythocypris and loxoconcha and xestoleberis hanaii the regression equation was applied to late pliocene and the resulting past water temperatures were compared to modern oceanographic data from water depths of 50 to 150 m in the sea of japan which is the paleodepth estimated to encompass the habitat of ostracode assemblages decreasing variation in the obtained past wt with the increase in the number of fossil ostracode valves from one to four suggests that more than four ostracode valves are required to reconstruct the mean annual wt using the equation established with c miurense and c sawanense thus the mean annual wt during the late pliocene based on analysis of four specimens ranged from 8 9 to 11 6 c which is similar to or slightly lower than the wt observed today

a new stylolite classification scheme to estimate compaction and local permeability variations we modeled the geometrical roughening of bedding parallel mainly layer dominated stylolites in order to understand their structural evolution to present an advanced classification of stylolite shapes and to relate this classification to chemical compaction and permeability variations at stylolites stylolites are rough dissolution seams that develop in sedimentary basins during chemical compaction in the zechstein 2 carbonate units an important lean gas reservoir in the southern permian zechstein basin in germany stylolites influence local fluid flow mineral replacement reactions and hence the permeability of the reservoir our simulations demonstrate that layer dominated stylolites can grow in three distinct stages an initial slow nucleation phase a fast layer pinning phase and a final freezing phase if the layer is completely dissolved during growth dissolution of the pinning layer and thus destruction of the stylolite s compaction tracking capabilities is a function of the background noise in the rock and the dissolution rate of the layer itself low background noise needs a slower dissolving layer for pinning to be successful but produces flatter teeth than higher background noise we present an advanced classification based on our simulations and separate stylolites into four classes 1 rectangular layer type 2 seismogram pinning type 3 suture sharp peak type and 4 simple wave like type rectangular layer type stylolites are the most appropriate for chemical compaction estimates because they grow linearly and record most of the actual compaction up to 40 mm in the zechstein example seismogram pinning type stylolites also provide good tracking capabilities with the largest teeth tracking most of the compaction suture sharp peak type stylolites grow in a non linear fashion and thus do not record most of the actual compaction however when a non linear growth law is used the compaction estimates are similar to those making use of the rectangular layer type stylolites simple wave like stylolites are not useful for compaction estimates since their growth is highly non linear with a very low growth exponent in the case where sealing material is collected at the tooth during dissolution stylolites can act as barriers for local fluid flow as they intensify sealing capabilities of pinning layers however the development of teeth and spikes offsets and thus destroys continuous stylolite seams so that the permeability across the stylolite becomes very heterogeneous and they are no continuous barriers this behavior is best shown in rectangular layer and seismogram pinning type stylolites that develop efficient fluid barriers at teeth tips but destroy sealing capabilities of layers by offsetting them at the flank leading to a permeability anisotropy along 2 d stylolite planes suture sharp peak stylolites can create fluid barriers if they collect enough sealing material however if the collecting material does not seal or if spikes offset the sealing material the stylolite leaks we propose that our classification can be used to realistically estimate chemical compaction in reservoirs and gives an indication on how heterogeneous the permeability of stylolites can be

north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles variations in the ratio of magnesium to calcium mg ca in fossil ostracodes from deep sea drilling project site 607 in the deep north atlantic show that the change in bottom water temperature during late pliocene 41 000 year obliquity cycles averaged 1 5 c between 3 2 and 2 8 million years ago ma and increased to 2 3 c between 2 8 and 2 3 ma coincidentally with the intensification of northern hemisphere glaciation during the last two 100 000 year glacial to interglacial climatic cycles of the quaternary bottom water temperatures changed by 4 5 c these results show that glacial deepwater cooling has intensified since 3 2 ma most likely as the result of progressively diminished deepwater production in the north atlantic and of the greater influence of antarctic bottom water in the north atlantic during glacial periods the ostracode mg ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from site 607 as well as derivation of a hypothetical sea level curve for the late pliocene and late quaternary the effects of dissolution on the mg ca ratios of ostracode shells appear to have been minimal

the physical oceanography of jones bank a mixing hotspot in the celtic sea abstract new measurements are presented of the currents and hydrography at jones bank in the celtic sea these measurements collected during the summer of 2008 identify a highly energetic internal wavefield generated by the local interaction of seasonally stratified flow with topography observations close to the bank crest reveal internal waves of up to 40 m amplitude approaching 50 of the local water depth these waves occur during spring periods and are predominantly associated with off bank tidal flow we provide evidence that these waves are the result of hydraulic control of the tidal currents which result in supercritical flow in the bottom mixed layer bml on the upper slopes of the bank the waning tide produces a transition from super to subcritical flow identifiable as a regular hydraulic jump on the bank slope microstructure measurements identify a turbulent bore associated with such jumps that increases bml turbulence by several orders of magnitude and produces a regular burst of enhanced mixing at the base of the ever present thermocline additional mixing in the surface mixed layer is provided during gale force conditions during the first of the two spring tides observed occurring at the start of our three week measurement period the average thermocline mixing rate during stormy spring tide conditions is 1 9 1 0 95 10 3 m 2 s 1 driven by both surface mixing and hydraulic jumps during the later calm spring period the average thermocline mixing rate is 3 3 1 7 10 4 m 2 s 1 dominated by jump associated events by comparison the intervening neap tide period produces no hydraulic jumps and is characterised by relatively calm weather a strong shear layer is however maintained during this quiet period sufficient to enhance thermocline turbulence by a factor 1000 above background levels a short lived peak in thermocline turbulence during the neap period produces diapycnal mixing as high as 1 6 10 2 m 2 s 1 however a more representative background thermocline mixing rate is 2 8 0 6 10 5 m 2 s 1

internal tidal mixing as a control on continental margin ecosystems we show that a breaking internal tide at a shelf edge is a fundamental control on the structural and functional properties of ecosystems contrasts in vertical mixing of nitrate between the shelf and the open ocean correspond with horizontal and vertical changes in phytoplankton communities with largest cells found in surface waters at the shelf edge intense fishing activity is commonly seen at continental shelf edges targeting spawning fish stocks we suggest that the internal tide a globally ubiquitous physical process at steep shelf edge bathymetry supports shelf edge fisheries by providing large celled phytoplankton for first feeding fish larvae the repeatability of the internal tide removes fish from the need to time spawning with a spring bloom also with large phytoplankton cells dominating particulate organic carbon export the internal tides could be an important influence on spatial and temporal variability in patterns of global carbon sequestration in deep water and sediments citation sharples j c m moore a e hickman p m holligan j f tweddle m r palmer and j h simpson 2009 internal tidal mixing as a control on continental margin ecosystems geophys res lett 36 l23603 doi 10 1029 2009gl040683

mg ca and sr ca of ostracod valves from living species of lake geneva abstract the mg ca and sr ca ratios of living ostracods belonging to 15 different species and sampled monthly over a one year cycle at five sites 2 5 13 33 and 70 m water depths in western lake geneva switzerland are compared to the oxygen and carbon isotope compositions measured on the same samples as well as to the temperature and chemical composition of the water 18 o h2o 13 c dic mg ca h2o and sr ca h2o at the time of ostracod calcification the results indicate that trace element incorporation varied at the species level mainly because of the ecological and biological differences between the different species life cycle micro habitat preference biomineralisation processes and the control thereof on trace element incorporation of the ostracods in littoral zones the mg ca and sr ca of ostracod valves increase as temperature and mg ca and sr ca of water increase during spring and summer hence reflecting mainly seasonal variations however given that for lake geneva the mg ca and sr ca of water also vary with temperature it is not possible to distinguish the effects of temperature from those of changes in chemical composition of water on the trace element content in ostracod valves results support that both water temperature and water mg ca and sr ca ratios control the final trace element content of cyprididae valves in contrast the trace element content of species living in deeper zones of the basin is influenced by variations in the chemical composition of the pore water for the infaunal species trace element content measured for these specimens cannot therefore be used to reconstruct the compositions of the water lake bottom in addition incorporation of mg and sr into the shell differs from one family sub family or even species to the other this suggests that the distinctive mg and sr partition coefficients for the analysed taxa result from different valve calcification strategies that may be phylogenetic

physical forcing and nutrient conditions associated with patterns of chl a and phytoplankton productivity in the southeastern bering sea during summer abstract measurements of nutrients primary 14 c productivity and new nitrate productivity collected in the southeastern bering sea in july and august 2004 together with measurements from july 1981 are used to characterize the regional production system during summer and to analyze the major physical and nutrient factors controlling biological patterns the patterns of surface productivity suggested by the two different summers were remarkably similar in the regions of data overlap and agree with recent compilations of summer conditions from remotely sensed data summer was characterized by low production in the middle and outer shelf associated with surface mixed layers that were stabilized by heat elevated productivity was restricted to regions associated with the surface expression of thermohaline fronts as well as to tidally mixed regions adjacent to and between the pribilof islands based on chl a and productivity measurements the biological impact of the shelf break front of the southeastern bering sea extends at least as far inshore as the pribilof islands the existence of elevated summer productivity associated with a recently identified shelf partition front between the pribilof domain and the middle shelf domain east of st paul island was confirmed and its thermohaline nature resulting from cumulative intrusions of slope derived water is described yearly estimates of new and primary productivity compiled for the various biophysical regimes range from 1800 mmol n m 2 yr 1 and 170 g c m 2 yr 1 at the shelf break front to less than 700 mmol n m 2 yr 1 and 100 g c m 2 yr 1 in oceanic and coastal waters we hypothesize that trace metals rather than macronutrients or grazing likely restrict the seaward extent of elevated production at the shelf break front iron may be supplied to the front by isopycnal mixing from deeper shelf waters that were in contact with sediments by extending elevated production throughout the summer the thermohaline and tidal fronts enhance the coupling of primary production to epipelagic food webs for the large populations of fish birds and mammals in the region changes in the intensity or location of these frontal systems may impact populations that forage in them from the nearby pribilof islands

a model for intergranular pressure solution in open systems abstract intergranular pressure solution ips represents a well known mechanism of bulk deformation and pore volume change especially in sedimentary rocks which has been documented in the field and reproduced in laboratory experiments theoretical descriptions of the process in terms of simple pressure solution creep laws can explain features such as grain size dependence of creep rates but have typically remained restricted to closed system conditions with negligible long range transport in the fluid phase and somewhat biased toward grain boundary diffusion controlled creep the recasting of the classical weyl rutter model of ips considered in this paper emphasizes open system conditions and the competition between diffusion and dissolution reaction rate processes the thermodynamic force which drives ips is expressed in terms of an effective grain boundary normal traction and a solute supersaturation this suggests the occurrence of a transition from ips to grain boundary healing at a certain level of supersaturation of the pore fluid although the process of healing is not studied here the explicit appearance of the solute concentration in the driving force highlights the coupling of the ips deformation process to the long range transport of dissolved material and the need to model the diagenesis of compacting sedimentary sequences accordingly the conceptual grain boundary model used in this paper is that of a fluid invaded grain to grain contact zone which is visualized to remain in a roughened state during continued ips the use of simple linear phenomenological rate laws for dissolution and grain boundary diffusion allows the ranges of rate control by dissolution or diffusion to be succinctly characterized in terms of the ratio of corresponding time constants the associated compaction behaviour is explored quantitatively in this paper by presenting solutions for the uniaxial and isotropic compaction creep strain vs time for a simple cubic packing of spheres

strontium content of ostracods indicates lacustrine palaeosalinity individual non marine ostracod valves contain sr in proportion to the sr content of their host lake water two commonly coexisting large planktonic species mytilocypris praenuncia and australocypris robusta have a sr distribution coefficient kd sr ca of 0 082 which is independent of temperature in the range 10 18 c if the relationship between salinity and the sr content of a hydrologically simple lake is known palaeosalinities can be calculated from fossil ostracods we present here palaeosalinities for the past 10 000 yr for lake keilambete victoria calculated from ostracod sr ca of fossil material which are in striking agreement with independent interpretations of palaeosalinity the range of salinity spans 14 95 we also show that a reliable quantitative continuous indicator of lacustrine palaeosalinity is important for the elucidation of continental palaeoenvironments for palaeoclimatology and archaeology and ocean continent climatic correlations and interactions

magnesium content of non marine ostracod shells a new palaeosalinometer and palaeothermometer abstract ostracods are microcrustaceans with calcitic carapaces each consisting of two valves or shells that grow by moulting and regeneration of sequentially larger valves up to nine times before reaching maturity the mg content of these valves is species dependent and is a function of their growth stage and the temperature salinity mg content and mg ca ratio of their host water newly formed partly calcified valves of the non marine nektic ostracod mytilocypris henricae have high mg contents 100 000 ppm mg in caco3 at individual shell weights of 2 g this relative mg content decreases as calcification proceeds until shell weights exceed 120 g whereupon the mg content is constant and useful as an indicator of the ostracod s environment mg ca ratios in individual ostracod valves from several species of the genera mytilocypris and australocypris from culture experiments and a series of australian lakes indicate that the valve s mg content increases as a function of increasing temperature and salinity within the range 11 25 c and for waters containing 24 2325 ppm mg the molar mg ca ratio in these ostracods fully calcified valves increases by 0 0015 or 370 ppm mg in caco3 per 1 c and per change of 125 ppm mg in solution for most mainland australian lakes a change in water composition of 125 ppm mg corresponds to a change of 3 5 in salinity for a given mg content of a lake the mg ca ratio of the water may vary within the range of common lacustrine values without significantly affecting mg uptake in the ostracod valves these relationships can provide palaeosalinities and or palaeotemperatures for ostracods recovered from continental sediments for mg partitioning an increase in temperature and salinity produce increased mg content in ostracods whereas for 18o fractionation in biogenic calcite an increase in temperature produces a decrease in 18o of the ostracod and an increase in salinity leads to an increase in 18o of the ostracod thus a combination of 18o and mg measurements on non marine ostracods should enable unique resolution of palaeotemperature and palaeosalinity variations

modeling and characterization of fracture patterns in the vatnajokull glacier the circular fracture pattern in the vatnajokull glacier generated by a recent subglacial volcanic eruption was analyzed using methods based on fractal analysis a crossover analysis based on estimates of the sampling bias showed that the fracture length was proportional to a power of the fracture area providing a quantitative characterization of patterns of interacting fractures a simple simulation model reproduces the most important visual and statistical characteristics of the observed fracture pattern the model can be used to understand and separate the roles of material properties deformation history and geometry in geological fracture processes

the formation and growth of pressure solution seams in clastic rocks a field and analytical study abstract pressure solution seams psss are closing mode structures of localised dissolution resulting in a volume reduction we present new observations constraining the processes by which psss initiate and grow in low porosity clastic rocks from southern ireland psss initiate as inter granular psss at quartz grain to grain contacts as quartz dissolves clay remains as a residue along the contacts as well as filling the adjacent pores to form incipient psss involving multiple grain boundaries further lengthening and thickening occurs by lateral linkage and transverse coalescence of neighbouring segments of incipient psss multiple pss segments are observed to concentrate in thin tabular zones that appear as single macroscopic psss visible in hand samples published numerical modelling results show the ability of both lateral and transverse growth of psss due to the presence of asperities on their flanks which confirm our interpretations based on our laboratory and field observations

variability in ostracod partition coefficients d sr and d mg implications for lacustrine palaeoenvironmental reconstructions living and sub recent ostracods were collected from four lakes and foul springs located in belgium france and spain characterized by low water mg ca ratios from 0 08 to 0 65 valves of ostracods belonging to cyprideis torosa candona neglecta c marchica and c candida have been extensively analysed for their magnesium and strontium contents with respect to calcium comparisons of these results are made using the same elements from the waters in which the ostracod valves calcified our results offer new and somewhat different interpretations with respect to the uptake of mg and sr in the calcitic ostracod valves these findings include the following 1 the partition coefficient l sr for ostracods belonging to the same genus candona is not a constant the observed variability in d sr values could be due to the rare of biological calcification although more investigations are necessary to assess the influence of this factor it is possible that some taxa grouped under the genus candona belong to a different genus 2 even at the species level cyprideis torosa the ostracod d sr cannot be considered to be constant at low water mg ca ratio 0 65 our d sr value for c torosa is higher than those determined by others for c torosa calcified in evolved marine water 3 the mg ca ratio of the water appears as a major factor influencing d mg for ostracods for low water mg ca values similar to 2 d mg drastically increases this phenomenon is also effective for inorganic calcite implying a non biologic effect that could be linked to mg2 adsorption consequently large variations in me content of fossil ostracod valves from selected lacustrine sequences with expected low water mg ca similar to 2 can be due to small variations in water mg ca c 1998 elsevier science b v all rights reserved

elastic strain energy as a control in the evolution of asymmetric pressure solution contacts subjecting a water rock system to load can enhance the rock solubility by 1 increasing normal pressure at the dissolving surface and 2 raising the elastic energy of the rock for pressure solution surfaces such as grain contacts solution seams and stylolites the pressure term in the chemical potential equation is orders of magnitude larger than the strain energy term thus the contribution of the strain energy to the overall solubility of the system is very small and it is most often ignored we show that the elastic strain energy at a pressure solution interface can have a profound effect on the manner in which it evolves the mechanism we propose is the following inducing a discontinuity in elastic strain energy across a pressure solution interface e g by changing its curvature can cause one side to become slightly more soluble than the other part of the material that is dissolved may diffuse the short distance across the fluid layer and raise the saturation in the vicinity of the less soluble surface if the fluid layer was already close to saturation the dissolution at the less soluble surface may be severely slowed down or even halted therefore although the strain energy difference across the interface has a negligible effect on the total amount of material that is dissolved there it may cause only one side to dissolve in this way the formation of stylolites can be facilitated by heterogeneities in the elastic strain energy difference along a pressure solution interface

the influence of rock heterogeneity on the scaling properties of simulated and natural stylolites abstract stylolites are among the most prominent deformation patterns in sedimentary rocks that document localized pressure solution recent studies revealed that stylolite roughness is characterized by two distinct scaling regimes the main goal of the present study is to decipher whether this complex scaling behavior of stylolites is caused by the composition of the host rock i e heterogeneities in the material or is governed by inherent processes on respective scales namely the transition from a surface energy to an elastic energy dominated regime as theoretically predicted for this purpose we have developed a discrete numerical technique based on a lattice spring model to simulate the competition between stress strain and dissolution during stylolite roughening we varied systematically the quenched noise initially present in the material which controls the roughening we also changed the size amount and dissolution rate of the heterogeneities introduced in our model and evaluated the influence on the scaling exponents our findings demonstrate that the roughness and growth exponents are independent of the exact nature of the heterogeneities we discovered two coinciding crossover phenomena in space and time that separate length and time scales for which the roughening process is either balanced by surface or elastic energies our observations are consistent with analytical predictions and with investigations quantifying the scaling laws in the morphology of natural stylolites the findings presented here can further be used to refine volume loss compaction estimates from the finite strain pattern of stylolites

horizontal advection and dispersion in a stratified shelf sea the role of inertial oscillations abstract the role played by inertial motions in horizontal dispersion within the thermocline of a broad mid latitude shelf sea is examined through the analysis of a deliberately released dye tracer our analysis is of the horizontal and vertical evolution over 40 h of a dye tracer injected into the seasonally stratified thermocline of the celtic sea on the nw european shelf the inferred diapycnal diffusivity was 1 3 1 5 10 5 m2 s 1 and the radial horizontal diffusivities of the depth integrated dye patch ranged from 1 9 to 4 0 m2 s 1 the inferred vertical diffusivity is in agreement with microstructure based estimates and the depth integrated horizontal diffusivity is broadly in agreement with previous dye release derived estimates made over similar scales and time periods asymmetry in the horizontal evolution of the dye patch was evident we argue that mean shear dispersion was responsible for lateral elongation of the dye patch particularly between hours 23 and 35 after release during which time horizontal diffusivity along the major axis ka exceeded that along the minor axis kb by more than a factor of 10 we further show that along patch shear was predominantly a result of differential advection between a deep residual flow to the south east and an oscillating wind driven surface ekman layer in this region of strong low frequency inertial shear a time dependent model of shear dispersion young et al 1982 was able to account for the observed rate of horizontal dispersion calculated on the target isopycnal surface

coupling between pressure solution creep and diffusive mass transport in porous rocks received 29 september 2000 revised 25 january 2002 accepted 30 january 2002 published xx month 2002 1 pressure solution is widely regarded as a mechanism of ductile deformation in the upper crust it is driven by stress differences and its rate is affected by temperature grain size and fluid chemistry pressure solution involves dissolution at grain contacts under high stress and precipitation at grain contacts on pore surfaces under low stress leading to porosity reduction by precipitation in the pore space or by grain indentation for a system closed at a grain scale pressure solution is traditionally described by a mechanism involving three steps 1 dissolution at intergranular interfaces 2 diffusion of solutes inside the contact between two grains and 3 precipitation on the surface of the grains in contact with the pore fluid in this paper we propose a model where we have added a fourth step to this process diffusive transport to other open pores to account for the macroscopic diffusion of solutes in pore fluids such that the deformation is not closed at the grain scale in this model differences in mineral solubility due to variations in stress and grain size produce concentration gradients which drive diffusive mass transport the interaction between pressure solution at a grain scale and transport over distances of several grains can lead to the amplification of initial porosity heterogeneities and subsequent localization of deformation regions of intense dissolution compact and form bands in close proximity to regions where the porosity reduction is mainly due to cementation pressure solution augmented by large scale diffusional transport will cause mass transport from fine grained to coarse grained rock volumes we show that such processes are important during both diagenesis of sediments and compaction of fault gouge index terms 3902 mineral physics creep and deformation 5114 physical properties of rocks permeability and porosity 8045 structural geology role of fluids 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords cementation compaction diagenesis gouge pressure solution transport citation gundersen e f renard d k dysthe k bjorlykke and b jamtveit coupling between pressure solution creep and diffusive mass transport in porous rocks j geophys res 107 0 xxxx doi 10 1029 2001jb000287 2002

growth of stylolite teeth patterns depending on normal stress and finite compaction abstract stylolites are spectacular rough dissolution surfaces that are found in many rock types they are formed during a slow irreversible deformation in sedimentary rocks and therefore participate to the dissipation of tectonic stresses in the earth s upper crust despite many studies their genesis is still debated particularly the time scales of their formation and the relationship between this time and their morphology we developed a new discrete simulation technique to explore the dynamic growth of the stylolite roughness starting from an initially flat dissolution surface we demonstrate that the typical steep stylolite teeth geometry can accurately be modelled and reproduce natural patterns the growth of the roughness takes place in two successive time regimes i an initial non linear increase in roughness amplitude that follows a power law in time up to ii a critical time where the roughness amplitude saturates and stays constant we also find two different spatial scaling regimes at small spatial scales surface energy is dominant and the growth of the roughness amplitude follows a power law in time with an exponent of 0 5 and reaches an early saturation conversely at large spatial scales elastic energy is dominant and the growth follows a power law in time with an exponent of 0 8 in this elastic regime the roughness does not saturate within the given simulation time our findings show that a stylolite s roughness amplitude only captures a very small part of the actual compaction that a rock experienced moreover the memory of the compaction history may be lost once the roughness growth saturates we also show that the stylolite teeth geometry tracks the main compressive stress direction if we rotate the external main compressive stress direction the teeth are always tracking the new direction finally we present a model that explains why teeth geometries form and grow non linearly with time why they are relatively stable and why their geometry is strongly deterministic while their location is random

effect of microcracking on pressure solution strain rate the gratz grain boundary model different but reasonable and well accepted assumptions made about grain boundary structure during pressure solution ps creep may easily have an effect of more than 10 orders of magnitude on the calculated ps deformation rate understanding of grain boundary structure during ps creep is therefore extremely important experimental evidence is presented in support of a grain boundary model previously proposed by a j gratz on the basis of observations on naturally deformed rocks in this model boundaries are assumed to have a static island channel network structure channels are located where microcracks intersect the boundary the rate of material transport is governed by thin film diffusion at the islands the model predicts that ps deformation rates are sensitive to the microcracking process ps rate is therefore essentially dependent on whether microcracking can occur and how intense the microcracking is these factors in turn depend on among others stress temperature effective pressure and crystallographic orientation the model qualitatively explains the observation made in experimentally and naturally deformed quartz rocks that the ps rate in single grains depends on crystallographic orientation the model predicts that sudden increases in stress or fluid pressure may lead to microcracking and subsequently many orders of magnitude increase in ps deformation rate

kinetic effects of microscale plasticity at grain boundaries during pressure solution 1 it is generally assumed in kinetic models for pressure solution in materials such as quartz that the effective dissolution rate coefficient in grain boundaries is equal to the conventional geochemical dissolution rate coefficient on a free surface however predictions based on this assumption usually overestimate both natural and experimental pressure solution rates even when evidence for dissolution rate control is strong a possible explanation for this discrepancy is that grain boundary structure and dissipative processes such as microscale plasticity in the grain boundary can decrease this effective rate coefficient on the basis of a simple grain boundary model assuming an island channel structure we have derived a preliminary model for the effect that dissipation by plastic deformation work hardening flow and creep of grain boundary islands has on dissolution controlled pressure solution rates comparing the predictions of this model with the experimental data on quartz pressure solution rates we see that microscale plasticity at grain boundary islands does slow down pressure solution and can help explain the discrepancies between observed and theoretical pressure solution rates when applied to pressure solution creep of sandstones or fault rocks in nature our model predicts that grain boundary plastic deformation in quartz might have a significant effect at depths beyond 9 10 km

nanogeochemistry nanostructures emergent properties and their control on geochemical reactions and mass transfers abstract nanogeochemistry a newly emerging research field attempts to understand geochemical reactions and mass transfers at nanometer scales especially with regards to the formation of nanostructures in geochemical systems emergent properties of these structures and their controls on geochemical processes the research also includes use of nanotechnology to design new materials and engineering approaches for effective natural resource extraction and environmental management at the core of this new research field is the concept that as the size of a material is reduced to nanometers novel physical or chemical properties of the material may emerge that can be drastically different from those of the corresponding bulk phase and the material properties then become size dependent nanostructures which frequently occur in geologic materials may directly control mineral phase stability mineral water interface chemistry geochemical reaction kinetics geo fluid migration and transport and even global biogeochemical cycles as a whole this paper aims to provide a comprehensive review of recent progress in nanogeochemical research the review is focused on two general types of nanostructures nano solid phases and nanopores nanofluids with an emphasis on the occurrence of each nanostructure in natural environments the associated emergent properties and the potential geochemical implications stemming from an increasing interest in shale gas research a special discussion is provided on gas oil disposition and migration in unconventional low permeability reservoirs wherein shale is treated as a nanocomposite material nanogeochemistry is a relatively young research field and much remains to be explored there is an urgent need for systematically characterizing specific nanostructures over the whole nanometer size range and developing a general theoretical framework for data analysis and synthesis there is also a need for developing experimental and modeling techniques to extrapolate the knowledge obtained from simple model systems to complex natural systems

an integrated model for transitional pressure solution in sandstones abstract a key aspect of the deformation of sedimentary rocks during diagenesis is pressure solution however it is often not clear why some rocks of a given mineralogy depth and pressure exhibit a great deal of pressure solution while very similar rocks under similar conditions do not to address such difficulties which we believe arise from the natural non linear physico chemical processes a quantitative model for pressure solution applied to sandstones has been developed this model subsumes various factors 1 pressure temperature and burial rate 2 grain size shape and packing of the mineral grains 3 the variability of water film thickness and coefficient of diffusion between any two grains in contact as a function of stress across the contact pore fluid pressure salinity ph and temperature in this study we distinguish several types of surface sites over quartz grains in a sandstone with corresponding differences in chemical potential thus allowing the diffusive transfer of matter from one site to another the contact between two grains is divided into two parts the actual true contact between two grains is a site of water film diffusion and the inclusions inside the contact the free face inclusion contacts are sites of free face pressure solution on the pore surface site precipitation occurs it is shown that a kinetics transition from a reaction limited deformation to a diffusion limited deformation occurs in the upper crust a geometric transition occurs too due to the textural evolution of the rock with deformation the main goal of this paper is to show the dynamics of the shifting importance of actual and free face inclusion contacts using a unified model including both features the result is a predictive model for porosity variations with depth due to pressure solution in sandstones

magnesium and strontium distributions within valves of a recent marine ostracode neonesidea oligodentata implications for paleoenvironmental reconstructions ostracodes are bivalved microcrustaceans that live in nearly all types of aquatic environments the chemical compositions of the calcified part of their carapaces are frequently used as an empirical proxy in paleoenvironmental reconstructions we investigated the compositions and the distribution of mg and sr within valves of a recent ostracode neonesideaoligodentata using an electron microprobe analyzer each of the investigated valves displayed large variations in mg and sr concentrations compared to the variations in ca and probably o there were no systematic chemical differences between right and left valves of each carapace and between male and female carapaces although there were some deviations the valves consisted of at least three chemical bands 1 a narrow usually 10 m high mg sr outer band outer band 2 a heterogeneous low mg sr middle band middle band and 3 a high mg low sr inner band inner band the high mg low sr inner band was well developed at the inner part of the margin including the marginal infold the high mg sr outer band is thought to be formed during the early stage of carapace formation when the calcification rate is high whereas other parts formed at later stages with a relatively slow calcification rates since bairdioidean ostracodes exemplified by neonesidea oligodentata have a long geological history and are abundant in many regions further studies on the mechanism of the mg ca distribution in these ostracodes will provide a suitable tool to estimate paleotemperatures in various marine environments

pressure solution in siliciclastic hp lt metamorphic rocks constraints on the state of stress in deep levels of accretionary complexes abstract the magnitude of differential stress in deep levels of accretionary complexes along convergent plate margins is poorly constrained by theoretical models and cannot be directly measured the only direct evidence to infer rheology and state of stress for such crustal settings is the microstructural memory of high pressure low temperature metamorphic rocks recorded during their crustal evolution microfabrics in hp lt metamorphic t 400 50 c p 10 2 kbar phyllites and quartzites of the phyllite quartzite unit on the island of crete southern aegean reveal 1 that progressive deformation was by pressure solution dissolution precipitation creep 2 that clastic quartz grains in the phyllites show no evidence for crystal plastic deformation during burial and exhumation 3 that the unilaterally rational 001 mica quartz phase boundaries were sites of strongly enhanced dissolution and 4 dislocation creep was restricted to a minor role in quartzites poor in mica consequently the magnitude of differential stress in relation to temperature in the phyllites has remained below the level required to drive dislocation creep throughout the history of burial to a depth of more than 30 km and subsequent exhumation currently available flow laws for quartzite indicate that the differential stress in the phyllites remained well below 15 mpa at temperatures around 400 c at a depth of 30 km this implies that the effective viscosity in deep crustal levels in forearc settings is much lower than that predicted by conventional models based on flow laws for dislocation creep

controls on ostracod valve geochemistry part 1 variations of environmental parameters in ostracod micro habitats abstract the variations of environmental conditions t ph 13 c dic dic 18 o mg ca and sr ca of ostracod habitats were examined to determine the controls of environmental parameters on the chemical and isotopic composition of ostracod valves results of a one year monitoring of environmental parameters at five sites with depths of between 2 and 70 m in lake geneva indicate that in littoral to sub littoral zones 2 5 and 13 m the chemical composition of bottom water varies seasonally in concert with changes in temperature and photosynthetic activity an increase of temperature and photosynthetic activity leads to an increase in 13 c values of dic and to precipitation of authigenic calcite which results in a concomitant increase of mg ca and sr ca ratios of water in deeper sites 33 and 70 m the composition of bottom water remains constant throughout the year and isotopic values and trace element contents are similar to those of deep water within the lake the chemical composition of interstitial pore water also does not reflect seasonal variations but is controlled by calcite dissolution aerobic respiration anaerobic respiration with reduction of sulphate and or nitrate and methanogenesis that may occur in the sediment pores relative influence of each of these factors on the pore water geochemistry depends on sediment thickness and texture oxygen content in bottom as well as pore water variations of chemical compositions of the ostracod valves of this study vary according to the specific ecology of the ostracod species analysed that is its life cycle and its micro habitat littoral species have compositions that are related to the seasonal variations of temperature 13 c values of dic and of mg ca and sr ca ratios of water in contrast the compositions of profundal species are largely controlled by variations of pore fluids along sediment depth profiles according to the specific depth preference of the species the control on the geochemistry of sub littoral species is a combination of controls for the littoral and profundal species as well as the specific ecology of the species

faunal and geochemical evidence for changes in intermediate water temperature and salinity in the western coral sea northeast australia during the late quaternary abstract ostracod assemblages and geochemical analyses of valves of specific ostracod taxa are used to reconstruct both qualitatively and quantitatively bottom water temperatures bwt for the last 100 000 years in the western coral sea the investigated core 51gc21 is situated in the lower reaches of the antarctic intermediate water at 1630 m water depth first we ran a principal coordinate analysis pcoa of 42 surface samples from the coral sea and then compared fossil assemblages with results of the pcoa in addition we selected well preserved speciments of the two genera krithe and bythocypris for mg ca analyses the mg ca is used to infer past changes in bwt for intermediate waters of the western coral sea results indicate large temperature fluctuations over the last 100 000 years of interest is the documentation that the bwt was similar to the present day temperature during part of isotope stage 3 comparison between our temperature record and the benthic foraminifer 18o record of core 51gc21 and with the 18o variations in seawater as reconstructed by labeyrie et al 1987 allowed assessment of past changes in bwt salinity and density thus we identify for the western coral sea three distinct periods on the basis of water mass density changes i e for isotope stage 1 stages 2 3 and 4 and stage 5 our temperature record also indicates a good correlation with the 60 s summer insolation calculations for the period between 25 000 yr b p and 75 000 yr b p comparison of our results from this study with other records from the western pacific the ontong java plateau in particular reveal the role of new guinea as an oceanographic barrier a wet phase recorded on continental australia coincides with our high bottom water temperature record for isotopic stage 3

solution transfer compaction of quartzites progress toward a rate law data on dissolution diffusion and growth in the quartz water system show that diffusion through grain boundary films is rate limiting for solution transfer and too slow to permit significant compaction in geologic time but that rates are more reasonable if the rough texture of natural grain boundaries is considered on the basis of scanning electron microscope observations a model is proposed that uses a hierarchical plumbing system in which grain boundaries consist of islands capped by grain boundary films separated by microcapillaries and connected to intergranular porosity a rate law based on such a model has an inverse grain size dependence up to a critical grain size that is large 10 cm under typical compaction conditions

melange a viscoelastic lattice particle model applicable to the lithosphere 1 this article introduces the software melange a 3d lattice particle hybrid model the software was specifically designed in order to simulate ductile visco elasto plastic deformation and can be used to study tectonic processes in the lithosphere from the micro to the macro scale melange is under an open source license the code takes both relevant yield mechanisms for the deformation of lithospheric material into account dynamic brittle failure and ductile creep where ductile creep is modeled as viscoelasticity the software considers effects of the local geology of the inherent disorder of geomaterials of rheological layering of the lithosphere and applies repulsion when the material fractures driving forces are the externally applied strain and the gravitational load melange applies an elastically isotropic regular 3d lattice with hcp geometry and next nearest neighbor interactions young s modulus viscosity material density and system size can be freely chosen poisson s ratio is restricted to values 0 25 the most important innovation of the software is a physically consistent scheme to model viscoelasticity in a lattice particle model the scheme couples the local lattice geometry to the time dependent volume conservative viscoelastic deformation of particles the procedure achieves the typical viscoelastic stress strain relationship the article incorporates a number of benchmark simulations where the model output is being tested and evaluated the results obtained with melange show strong similarities with the benchmark values e g stress fields in crack vicinity geologically relevant examples include structures associated with the brittle ductile transition growth of wing cracks and brittle graben formation

tidal front entrainment and retention of fish larvae on the southern flank of georges bank abstract from a grid of stations across the southern flank of georges bank in may 1997 larval haddock and cod were observed to be concentrated across the tidal front in a band 10 20 km wide several cross bank ctd and acoustic doppler current profiler adcp sections indicated a narrow 35 m cross isobath residual flow 0 6 1 2 cm s

fishing and the oceanography of a stratified shelf sea fishing vessel position data from the vessel monitoring system vms were used to investigate fishing activity in the celtic sea a seasonally stratifying temperate region on the shelf of northwest europe the spatial pattern of fishing showed that three main areas are targeted 1 the celtic deep an area of deeper water with fine sediments 2 the shelf edge and 3 an area covering several large seabed banks in the central celtic sea data from each of these regions were analysed to examine the contrasting seasonality of fishing activity and to highlight where the spring neap tidal cycle appears to be important to fishing the oceanographic characteristics of the celtic sea were considered alongside the distribution and timing of fishing illustrating likely contrasts in the underlying environmental drivers of the different fished regions in the central celtic sea fishing mainly occurred during the stratified period between april and august based on evidence provided in other papers of this special issue we suggest that the fishing in this area is supported by 1 a broad increase in primary production caused by lee waves generated by seabed banks around spring tides driving large supplies of nutrients into the photic zone and 2 greater concentrations of zooplankton within the region influenced by the seabed banks and elevated primary production in contrast while the shelf edge is a site of elevated surface chlorophyll previous work has suggested that the periodic mixing generated by an internal tide at the shelf edge alters the size structure of the phytoplankton community which fish larvae from the spawning stocks along the shelf edge are able to exploit the fishery for nephrops norvegicus in the celtic deep was the only one to show a significant spring neap cycle possibly linked to nephrops foraging outside their burrows less during spring tides more tentatively the fishery for nephrops correlated most strongly with a localised shift in the tidal current polarisation suggesting that the muddy seabed required by nephrops is controlled by rotational constraints on the extent of the bottom boundary layer

simulation and characterization of fracture patterns in glaciers during drainage of subglacial lakes the surface of the glacier subsides and fractures generating a homogeneous circular fracture pattern on the rim of the resulting depression we have analyzed several fracture patterns around the skafta cauldron on iceland a regular fracture spacing was observed on the cauldron rim indicating that the region was subjected to a uniform strain in this region standard image analysis techniques were applied to find the lengths l and open areas a of the fractures we demonstrate that an understanding of sampling biases allows a scaling relation l a to be established and the exponent to be determined this relation provides a quantitative characterization of interactions between fractures in the population the value of is higher for that observed for laboratory experiments on clay but the uncertainties do not rule out a universal behavior which applies to ice rock and all other solids the size distribution of fractures did not display a similarly simple crossover behavior and a power law scaling relation could not be established without a better understanding of the crossovers for large fractures we introduce a simple simulation model that reproduces the most important visual and statistical properties of the glacier fracture pattern the direct comparison validates the use of the model to simulate geological fracturing processes

mg ca ratios in the shells of cultured specimens and natural populations of the marine ostracode xestoleberis hanaii crustacea abstract we studied mg ca ratios in the shells of the shallow water ostracode xestoleberis hanaii ishizaki 1968 ishizaki k 1968 ostracodes from uranouchi bay kochi prefecture japan tohoku university science report second series geology 40 1 1 45 in laboratory cultured and field collected samples x hanaii was cultured in our laboratory from a 7 to adult stage under controlled temperatures 15 28 c results of the culture experiments show that the mg ca ratio of x hanaii is strongly correlated with water temperature within the temperature range of 15 28 c in the field collected samples seasonally fluctuating mg ca ratios of their shells parallel the variation in the seasonal seawater temperature and the water temperature estimated from the mean value of the adult stage samples collected on any given date agreed quite well with the average water temperature for the period of 8 days prior to the collection date based on the changes in mg ca ratios and shell morphology in the course of ontogeny we suggest that mg is contained in the organic matter which is one of the shell components that form the network or the framework within which the calcite crystals are formed

pervasive pressure solution transfer in a quartz sand the kinetics of deformation of a quartz aggregate by pervasive pressure solution can be under certain conditions of temperature and grain size strongly dependent upon the diffusivity of silica into the grain to grain contacts an analysis of the factors affecting this key parameter and less well constrained in the analysis of the problem of rock deformation by pressure solution is presented this analysis is based on recent advances on studying silica surfaces and particularly on the existence of a silica gel layer on the silica surfaces undergoing dissolution by reinvestigating the electroviscous effect occurring at the grain to grain contact the present analysis shows that the diffusivity of silica at the grain to grain contacts is likely to be relatively similar to that in the bulk pore water maybe 1 order of magnitude smaller but not more this contradicts the previous work by rutter 1976 which has been the key reference used in many subsequent papers to justify an extremely low value for the diffusivity of silica at the grain to grain contacts 5 orders of magnitude smaller than the diffusivity of silica in free water this finding has dramatic implications concerning the deformation rate of quartz sands and sandstones by pressure solution in sedimentary basins with regard to 1 the limiting step affecting the kinetics of the process diffusion of the solute or dissolution precipitation chemistry and 2 the existence of a thermodynamic equilibrium state when deformation by pressure solution occurs over geological timescales a poroviscoplastic model is used to describe deformation associated with pervasive pressure solution transfer in quartz sands this model is shown to be consistent with the current state of knowledge of the surface chemistry of silica in addition the comparison between this model and both laboratory and field data is rather good

an s coordinate density evolving model of the northwest european continental shelf 2 seasonal currents and tides the barotropic tides and the residual currents from a year long run of a three dimensional baroclinic model the proudman oceanographic laboratory three dimensional baroclinic b grid model applied to the northwest european shelf are investigated m2 currents and elevations differ from observations by typically 0 114 m s 1 and 0 143 m these errors are dominated by a number of large values at the coast the density component of the residual currents is derived from the difference between the full model and wind and tide only model runs this demonstrates the importance of density driven currents in a number of regions particularly in the norwegian trench around the st george s channel to the east of the shetland isles and in the river plumes however volume fluxes show the mass budget of the north sea is primarily determined by the wind driven circulation calculations of the dynamic balance in the model show the significance of friction and or advective effects on a timescale of days at a number of locations e g the dover strait and in the central north sea however the monthly mean currents are in geostrophic balance over virtually the whole domain ageostrophic components adjust the surface and isopycnal slopes to restore this balance on comparatively short timescales particular attention is given to the western boundary and we demonstrate that variations in the imposed temperature and salinity here have only a limited effect on the shelf current meters on the hebrides shelf show that the model produces reasonably accurate residual currents but also that this agreement is degraded by the boundary condition on porcupine bank