eddy diffusivities estimated from observations in the labrador sea eddy diffusivities in the labrador sea ls are estimated from deep eddy resolving float trajectories moored current meter records and satellite altimetry a mean residence time of 248 days in the central ls is observed with several floats staying for more than 2 years by applying a simple random walk diffusion model the observed distribution of float residence times in the central ls could be explained by a mean eddy diffusivity of about 300 m2 s 1 estimates from float trajectories themselves and from moored current meter records yield significantly higher eddy diffusivities in the central ls of 950 1100 m2 s 1 this discrepancy can be explained by an inhomogeneity of the eddy diffusivity at middepth with high low values in the central ls region between central ls and deep labrador current which could be conjectured from the mean altimetric eddy kinetic energy eke distribution the different diffusivities explain both 1 a fast lateral homogenization of water masses in the central ls and 2 a weak exchange between central ls and boundary current the mean lagrangian length scale of 11 5 0 7 km as estimated from deep float trajectories is only slightly larger than the mean rossby radius of deformation 8 8 km largest eddy diffusivities within the central ls are associated with strong eddy drifts rather than with large swirl velocities and associated large eke between central ls and deep labrador current which could be conjectured from the mean altimetric eddy kinetic energy eke distribution the different diffusivities explain both 1 a fast lateral homogenization of water masses in the central ls and 2 a weak exchange between central ls and boundary current the mean lagrangian length scale of 11 5 0 7 km as estimated from deep float trajectories is only slightly larger than the mean rossby radius of deformation 8 8 km largest eddy diffusivities within the central ls are associated with strong eddy drifts rather than with large swirl velocities and associated large eke

impact of shelf basin freshwater transport on deep convection in the western labrador sea abstractfreshwater exiting the arctic ocean through the canadian arctic archipelago caa has been shown to affect meridional overturning circulation and thereby the global climate system however because of constraints of spatial resolution in most global ocean models neither the flow of low salinity water through the caa to the labrador sea nor the eddy activity that may transport freshwater from the shelf to areas of open ocean convection can be directly simulated to address these issues this study uses a high resolution ice ocean model of the pan arctic region with a realistic caa and forced with realistic atmospheric data this model resolves conditions in the arctic ocean upstream of the labrador sea and is coupled to a thermodynamic dynamic sea ice model that responds to the atmospheric forcing the major shelf basin exchange of liquid freshwater occurs south of hamilton bank whereas the largest ice flux occurs in the northwest of the basin freshwater flux anomalies entering the labrador sea

hydrothermal mineralising systems as chemical reactors wavelet analysis multifractals and correlations abstract hydrothermal mineralising systems are discussed as large open flow chemical reactors held far from equilibrium during their life time by deformation and the influx of heat fluid and dissolved chemical species as such they are nonlinear dynamical systems and need to be analysed using the tools that have been developed for such systems hydrothermal systems undergo a number of phase transitions during their evolution and this paper focuses on methods for characterising these transitions in a quantitative manner and establishing whether they resemble either abrupt or continuous critical phase transitions or whether they have some other kind of nature critical phase transitions are characterised by long range correlations for some parameter characteristic of the system power law probability distributions so that there is no characteristic length scale and a high sensitivity to perturbations the transitions undergone in mineralised hydrothermal systems are i widespread non localised mineral alteration involving exothermic mineral reactions that produce hydrous silicate phases carbonates and iron oxides ii strongly localised veining brecciation and or stock work formation iii a series of localised endothermic mineral reactions involving the formation of non hydrous silicates sulphides and metals such as gold iv multiple overprinting repetitions of transitions ii and iii we quantify aspects of these transitions in some gold deposits from the yilgarn craton of western australia using wavelet transforms this technique is convenient and fast it enables one to establish if the transition is multifractal and if so quantify the multifractal or singularity spectrum and to determine the scale dependence of long range correlations or anti correlations other aspects of the spectrum enable quantitative distinctions between sub critical critical and super critical systems the availability of long drill holes with detailed chemical analyses and mineral abundances derived from hyperspectral data enables individual ore bodies to be characterised rapidly in a quantitative manner and constraints placed on whether the various transitions are possibly critical or of some other form we also present some simple nonlinear models including numerical simulation self organised branching and multiplicative cascade processes that produce the multifractal character and correlation scaling relations observed in these data sets distinctions between systems that are strongly and weakly mineralised are discussed

hydraulic fracturing after water pressure control blasting for increased fracturing traditional hydraulic fracturing techniques generally form main hydraulic cracks and airfoil branch fissures but main hydraulic cracks are relatively few in number hydraulic fracturing after water pressure control blasting can transform the structure of coal and rock mass experiments prove that it is an effective method for increasing the number and range of hydraulic cracks as well as for improving the permeability of coal seams the technical principle is as follows first a hole is drilled in the coal seam and is injected with a gel explosive a mining water proof explosive then water is injected into the hole to seal it at low enough pressure to prevent cracks from forming third water pressure blasting is done by detonating the explosive the water shock waves and bubble pulsations produced by the explosion cause a high strain rate in the rock wall surrounding the hole when the stress imposed on the rock wall surrounding the hole exceeds its dynamic critical fracture strength the surrounding rock breaks and numerous circumferential and radial fractures propagate outward lastly water injection processes such as general injection pulse injection and or cyclic injection are carried out to promote hydraulic fracturing depending on the fissure water pressure detonation fissures continue to expand and additional hydraulic fractures with a wider range are formed under the effect of detonation pressure joints and fissures in the coal mass open and propagate leading to reduced adhesive forces on structural surfaces and thereby enhancing coal cutting therefore this method improves the permeability of the coal seam effectively weakens the strength of the coal and rock mass and reduces the surrounding rock stress of the weakened area effectively solving the problem of having a small number of big cracks it is a useful technical approach for improving top coal caving preventing rock burst preventing coal and gas outbursts and raising the gas extraction efficiency in colliery

stress relief coalbed methane drainage by surface vertical wells in china abstract this paper summarizes the status of engineering practice technology and research related to stress relief coalbed methane cbm drainage using surface wells in china during the past 10 years comments are provided on the theory and technical progress of this method in high gas mining areas such as the huainan huaibei and tiefa mining areas characterized by heavily sheared coals with relatively low permeability stress relief cbm surface well drainage has been successfully implemented and has broad acceptance as a cbm exploitation technology the fundamental theories underpinning stress relief cbm surface well drainage were established in china and include elements relating to 1 rock layer deformation theory vertical zoning and horizontal partitioning and the change in the stress condition in mining stopes 2 a theory regarding an abscission circle in the development of mining horizontal abscission fracture and vertical broken fracture in overlaying rocks and 3 the theory of stress relief inducing permeability increase in protected coal seams during mining and the gas migration accumulation theory of stress relief cbm surface well drainage three kinds of technical drainage modes are described protected seam surface well drainage in areas influenced by mining represented mainly in the huainan mining area gob surface well drainage most prominently in the tiefa mining areas and the multipurpose surface well drainage used in the huaibei mining areas serial well allocation in which wells are used for different purposes as extraction and mining proceeds and well bore configurations and designs suitable for this purpose are described the development and utilization of cbm is significant to energy saving emission reduction and to ensure safety in coal production

instantaneous outbursts in underground coal mines an overview and association with coal type instantaneous outbursts in underground coal mines have occurred in at least 16 countries involving both methane ch4 and carbon dioxide co2 the precise mechanisms of an instantaneous outburst are still unresolved but must consider the effects of stress gas content and physico mechanical properties of the coal other factors such as mining methods e g development heading into the coal seam and geological features e g coal seam disruptions from faulting can combine to exacerbate the problem prediction techniques continue to be unreliable and unexpected outburst incidents resulting in fatalities are a major concern for underground coal operations gas content thresholds of 9 m 3 t for ch4 and 6 m 3 t for co2 are used in the sydney basin to indicate outburst prone conditions but are reviewed on an individual mine basis and in mixed as situations data on the sorption behaviour of bowen basin coals from australia have provided an explanation for the conflicting results obtained by coal face desorption indices used for outburst proneness assessment a key factor appears to be different desorption rates displayed by banded coals which is supported by both laboratory and mine site investigations dull coal bands with high fusinite and semifusinite contents tend to display rapid desorption from solid coal for a given pressure drop the opposite is true for bright coal bands with high vitrinite contents and dull coal bands with high inertodetrinite contents consequently when face samples of dull fusinite or semifusinite rich coal of small particle size are taken for desorption testing much gas has already escaped and low readings result the converse applies for samples taken from coal bands with high vitrinite and or inertodetrinite contents in terms of outburst potential it is the bright vitrinite rich and the dull inertodetrinite rich sections of a coal seam that appear to be more outburst prone this is due to the ability of the solid coal to retain gas even after pressure reduction creating a gas content gradient across the coal face sufficient to initiate an outburst once the particle size of the coal is reduced rapid gas desorption can then take place c 1998 elsevier science

an expanded de wijs model for multifractal analysis of mineral production data hydrothermal ore deposits form by enriching elements and minerals from background values to very high concentrations in small volumes of the crust the de wijs model provides a simple and widely used mathematical description of this process however it does not account for the increase in density which generally attends the formation of high specific gravity minerals in many mineral deposits we present an expanded version of the de wijs model to investigate the distribution of ore tonnage as well as grade the expanded model generates a log normal relationship between ore tonnage and grade continuous multifractal analysis of results from the new model using the method of moments technique predicts that ore grades are multifractal as in the original de wijs model but that ore tonnage values are not multifractal production data from vein hosted gold deposits in the archaean zimbabwe craton display the log normal relationship between ore tonnage and grade the multifractal nature of ore grade and the nonmultifractal nature of ore tonnage which are generated in the expanded de wijs model

rock burst process of limestone and its acoustic emission characteristics under true triaxial unloading conditions abstract the rock failure process is associated with acoustic emission ae hence violent rock failure processes such as rock burst under different stress paths in laboratory can be studied using the ae monitoring technique in this paper single face dynamic unloading tests under true triaxial condition were carried out for paleozonic marine sedimentation limestone samples produced by blocks cored from 1140 m depth in jiahe coal mine of china frequency spectra analysis was conducted for the full wave ae data and figures showing the relationship of frequency amplitude of ae signals in rock burst stages were obtained the dynamical damage process and characteristics of limestone under the test condition are summarized it is found from the fast fourier transformation fft analysis of the ae signals that there exist two main frequency ranges i e lower 60 100 khz and higher 170 190 khz for the samples when the limestone samples are under relatively lower stress the ae signals are characterized by high frequency and low amplitude as the stress increases the ae signals tend to shift more towards a signature of high amplitude near the bursting failure of the rock samples it is observed that there are much higher amplitude and lower frequency events the ae accumulated energy release rapidly increases from the unloading state of the rock samples to its failure the dynamic unloading test facility provides a useful tool to gain an insight into the characteristics of rock bursts

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

quasi decadal salinity fluctuations in the labrador sea abstract the quasi decadal salinity fluctuations in the upper 300 m of the labrador sea are investigated by partitioning all available salinity station data since 1948 by region and bottom depth there are major freshwater anomalies in the early 1970s the great salinity anomaly mid 1980s and early 1990s these vary in amplitude throughout the region being least on the shelf and greatest over the slope region near the labrador current the labrador sea cannot be considered a simple conduit for freshwater anomalies originating in the east greenland current there is evidence that local processes modulate the anomaly the freshwater anomalies in the labrador current are approximately twice as large as those in the east greenland current the baffin island current flowing southward through the western davis strait is the only local source of freshwater with sufficient volume to account for this increase the propagation speed 2 3 cm s 1 of the anomaly along the labrador sea margin is much less than the

impact of co2 geological sequestration on the nucleation of earthquakes 1 can co2 storage cause earthquakes what is the maximum possible earthquake magnitude resulting from co2 injection here as a theoretical case study we investigate these questions using coupled hydromechanical modeling with multiphase flow and seismological variables for quantifying earthquake magnitude and energy our simulations consider transient fluid flow and stress coupling and the evolution of fault properties we simulate co2 injection into a reservoir caprock system bounded by a subvertical normal fault subjected to different extensional stress regimes and over a range of initial fault permeability values for our assumed system and injection rate the simulation results show that sudden stress drop and fault slip primarily initiated along the fault portion intersecting the storage reservoir after a few months of injection when a sufficiently high reservoir pressure has been reached the size of the rupture area and consequently the earthquake magnitude and energy depends on initial horizontal to vertical stress ratio and fault permeability which strongly influences the size of the pressurized area and subsequent stress variations

recent variability of the north atlantic thermohaline circulation inferred from surface heat and freshwater fluxes abstract an annual mean surface forced component of the north atlantic thermohaline circulation thc in density space surf is diagnosed from observed surface heat and freshwater fluxes the climatological mean of surf over 1980 97 indicates steady overturning rates for those water masses that are principally formed through surface buoyancy forcing 8 sv of greenland sea deep water gsdw 4 sv of labrador sea water lsw and 4 sv of 18 water stmw obtained for each year over 1980 97 surf reveals interannual to decadal variability in the renewal and overturning of these water masses the total surface forced overturning rate varies in the range 10 20 sv reaching peak values in 1989 90 and generally decreasing over the period 1990 97 more dramatic changes are apparent in the overturning of different water masses the overturning of stmw exhibits large amplitude interannual variability a background positive trend over 1980 97 is dominated by variance of 13 4 sv by contrast the overtur

on the connection between dense water formation overturning and poleward heat transport in a convective basin an isopycnal two layer idealized model for a convective basin is proposed consisting of a convecting interior region and a surrounding boundary current buoyancy and wind driven parameterized eddy fluxes govern the exchange between the two to balance the interior buoyancy loss the boundary current becomes denser as it flows around the basin geostrophy imposes that this densification be accompanied by sinking in the boundary current and hence by an overturning circulation the poleward heat transport associated with convection in the basin can thus be viewed as a result of both an overturning and a horizontal circulation when adapted to the labrador sea the model is able to reproduce the bulk features of the mean state the seasonal cycle and even the shutdown of convection from 1969 to 1972 according to the model only 40 of the poleward heat buoyancy transport of the labrador sea is associated with the overturning circulation an exact solution is presented for the linearized equations when changes in the boundary current are small numerical solutions are calculated for variations in the amount of convection and for changes in the remotely forced circulation around the basin these results highlight how the overturning circulation is not simply related to the amount of dense water formed a speeding up of the circulation around the basin due to wind forcing for example will decrease the intensity of the overturning circulation while the dense water formation remains unvaried in general it is shown that the fraction of poleward buoyancy or heat transport carried by the overturning circulation is not an intrinsic property of the basin but can vary as a result of a number of factors

buoyant eddies entering the labrador sea observed with gliders and altimetry abstract intense buoyant anticyclonic eddies spawned from the west greenland boundary current were observed with high resolution autonomous seaglider hydrography and satellite altimetry as they entered the labrador sea interior surveys of their internal structure establish the transport of both low salinity water in the upper ocean and warm saline irminger water at depth the observed eddies can contribute significantly to the rapid restratification of the labrador sea interior following wintertime deep convection these eddies have saline cores between 200 and 1000 m low salinity cores above 200 m and a velocity field that penetrates to at least 1000 m with 0 1000 m average speeds exceeding 40 cm s 1 their trajectory together with earlier estimates of the gyre circulation suggests why the observed region of deep convection is so small and does not occur where wintertime cooling by the atmosphere is most intense the cyclostrophic surface velocity field of the anticylones from satellite altimetry

meso and submesoscale structure of a convecting field abstract intensive data collection in the region of the labrador sea northwest of former ocean weather station bravo during the winter of 1998 allowed examination of the meso and submesoscale structure during active convection data used include shipboard ctds shipboard underway data isobaric ctd profiling floats and high drag floats whose trajectories were approximately lagrangian in the horizontal and vertical directions on the mesoscale o 20 km horizontal variability was nearly 1 c and 0 1 psu an anticyclonic eddy of 40 km diameter was found on a smaller scale o 5 km variability of 0 04 psu and 0 3 c was found by utilizing data from fully lagrangian floats this smaller scale field was found to be organized into eddies of 1 12 km radius both cyclonic and anticyclonic features were found with the anticyclones being larger this observation may explain the excess of anticyclones reported in previous studies having lower spatial resolution these features were unsteady with an anticyclone

characterization of the co2 fluid adsorption in coal as a function of pressure using neutron scattering techniques sans and usans abstract small angle neutron scattering techniques have been applied to investigate the phase behavior of co2 injected into coal and possible changes in the coal pore structure that may result from this injection three coals were selected for this study the seelyville coal from the illinois basin ro 0 53 baralaba coal from the bowen basin ro 0 67 and bulli 4 coal from the sydney basin ro 1 42 the coals were selected from different depths to represent the range of the underground co2 conditions from subcritical to supercritical which may be realized in the deep subsurface environment the experiments were conducted in a high pressure cell and co2 was injected under a range of pressure conditions including those corresponding to in situ hydrostatic subsurface conditions for each coal our experiments indicate that the porous matrix of all coals remains essentially unchanged after exposure to co2 at pressures up to 200 bar 1 bar 105 pa each coal responds differently to the co2 exposure and this response appears to be different in pores of various sizes within the same coal for the seelyville coal at reservoir conditions 16 c 50 bar co2 condenses from a gas into liquid which leads to increased average fluid density in the pores pore with sizes r 1 105 r 1 104 a pore 0 489 g cm3 as well as in small pores with size between 30 and 300 a pore 0 671 g cm3 these values are by a factor of three to four higher than the density of bulk co2 co2 under similar thermodynamic conditions co2 0 15 g cm3 at the same time in the intermediate size pores with r 1000 a the average fluid density is similar to the density of bulk fluid which indicates that adsorption does not occur in these pores at in situ conditions for the baralaba coal 35 oc 100 bar the average fluid density of co2 in all pores is lower than that of the bulk fluid pore co2 0 6 neutron scattering from the bulli 4 coal did not show any significant variation with pressure a phenomenon which we assign to the extremely small amount of porosity of this coal in the pore size range between 35 and 100 000 a

permeability evolution during progressive deformation of intact coal and implications for instability in underground coal seams abstract we report measurements of deformation strength and permeability evolution during triaxial compression of initially intact coals permeability is continuously measured by the constant pressure differential method together with axial and volumetric strains for both water h2o and strongly adsorbing carbon dioxide co2 gas strength and young s modulus increase with increasing confining stress and permeability is hysteretic in the initial reversible deformation regime as deviatoric stress and strain increase permeability first decreases as pre existing cleats close and then increases as new vertical dilatant microcracks are generated post peak strength the permeability suddenly increases by 3 4 orders of magnitude during loading the inflection point where permeability begins to increase occurs earlier than the turning point of volumetric strain which may be explained by the competing processes of axial crack opening and closure of oblique and transverse cracks the generation of these vertical microcracks does not enhance gas migration in the horizontal direction but will accelerate the rate of gas desorption and weaken the coal based on this mechanistic observation we propose a process based model for bursting in underground coal seams horizontal and vertical stresses redistribute ahead of the mining face immediately after the excavation and influence pore pressure permeability and desorption rate due to this redistribution the zone closest to the mining face may experience tensile failure interior to this zone a region may develop with gas overpressures induced by desorption and this may contribute to the occurrence of coal and gas outbursts beyond this an overstressed zone may initiate shear failure driven by gas pressures if the desorption rate outstrips the rate of drainage we discuss the implications of this on the instability of coal seams to co2 injection and the potential for induced fault slip

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

nonlinear analysis of natural folds using wavelet transforms and recurrence plots three dimensional models of natural geological fold systems established by photogrammetry are quantified in order to constrain the processes responsible for their formation the folds are treated a

the effect of gas sorption on the strength of coal abstract the sudden violent failure of coal accompanied by the release of large volumes of gas is known as an outburst and represents a major coal mining hazard one parameter affecting coal outbursts is the coal strength provided that the pore fluid is inert the strength will decrease with increasing pore gas pressure in accordance with the law of effective stress however the gases involved in outbursts carbon dioxide and or methane are not inert they sorb onto the coal surfaces reducing the surface energy and thus theoretically at least further reduce the strength of the coal the tensile strength of two coals have been measured in sorbing carbon dioxide and nonsorbing helium atmospheres up to pore gas pressures of 3 5 mpa it has been shown that for these coals gas sorption produces no significant reduction in coal strength at the 95 confidence level hence if these results are representative of all coals it would appear that the strength reduction due to gas sorption is not a factor that need be taken into account in the consideration of coal outbursts

mechanisms behind the temporary shutdown of deep convection in the labrador sea lessons from the great salinity anomaly years 1968 71 abstractfrom 1969 to 1971 convection in the labrador sea shut down thus interrupting the formation of the intermediate dense water masses the shutdown has been attributed to the surface freshening induced by the great salinity anomaly gsa a freshwater anomaly in the subpolar north atlantic the abrupt resumption of convection in 1972 in contrast is attributed to the extreme atmospheric forcing of that winter here oceanic and atmospheric data collected in the labrador sea at ocean weather station bravo and a one dimensional mixed layer model are used to examine the causes of the shutdown and resumption of convection in detail these results highlight the tight coupling of the ocean and atmosphere in convection regions and the need to resolve both components to correctly represent convective processes in the ocean they are also relevant to present day conditions given the increased ice melt in the arctic ocean and from the greenland ice sheet the analysis herein shows that the shutdown was initiat

ventilation and transformation of labrador sea water and its rapid export in the deep labrador current a model of the subpolar north atlantic ocean is used to study different aspects of ventilation and water mass transformation during a year with moderate convection intensity in the labrador sea the model realistically describes the salient features of the observed hydrographic structure and current system including boundary currents and recirculations ventilation and transformation rates are defined and compared the transformation rate of labrador sea water lsw defined in analogy to several observational studies is 6 3 sv sv 106 m3 s 1 in the model using an idealized ventilation tracer mimicking analyses based on chlorofluorocarbon inventories an lsw ventilation rate of 10 sv is found differences between both rates are particularly significant for those water masses that are partially transformed into denser water masses during winter the main export route of the ventilated lsw is the deep labrador current lc backward calculation of particle trajectories demonstrates that about one half of the lsw leaving the labrador sea within the deep lc originates in the mixed layer during that same year near the offshore flank of the deep lc at about 55 w the transformation of lsw begins in january and is at a maximum in february march while the export of transformed lsw out of the central labrador sea continues for several months lsw generated near the boundary current is exported more rapidly with maximum transport rates during march april within the deep lc

folding with thermal mechanical feedback folding of viscous layered rocks is traditionally viewed as an instability arising from viscosity differences between layers this approach derives from biot and for purely viscous materials predicts the growth of single wavelength systems the dominant wavelength is sensitive to layer thickness the viscosity ratio between the layers the amount of shortening and the boundary conditions this paper presents one alternative theory of folding to that of biot and addresses the deformation of elastic viscous materials where the viscosity ratio between layers is small and biot theory predicts folds will not form such ratios are consistent with situations in the mid to lower crust as indicated by experimental data folding results from the coupling between temperature dependent viscosity and heat generated by deformation the result is weakening in the hinges of embryonic folds and subsequent buckling this process is distinct from the biot buckling process the structures that develop resemble natural structures in that folds develop at a range of length scales hinges undergo strong thickening and axial plane crenulations form this approach is grounded in non equilibrium thermodynamics the coupling of deformation to fluid flow and chemical reactions is explored as part of a unified framework for rock deformation processes

the formation of labrador sea water part i large scale processes abstract data obtained in the western labrador sea during march 1976 by hudson are analysed to show that new labrador sea water was being formed at this time on the basis of hydrographic and moored current meter data it is hypothesized that a 200 km scale cyclonic gyre forms in winter in the western labrador sea and that this gyre retains the developing deep mixed layers in this general area long enough for the transformation to labrador sea water to take place using a model it is demonstrated that water columns found along the western boundary of the labrador sea can be modified by cooling evaporation and mixing to form deep mixed layers with the properties of labrador sea water approximately 105 km3 of new labrador sea water was formed in 1976 an estimate that is consistent with earlier estimates of mean annual production rates this water 2 9 c 34 84 is some 0 6 c cooler and 0 06 fresher than that defined by lazier 1973 from his data collected in 1966 the variation of labrador sea water

the relative roles of folding and faulting in controlling gold mineralization along the deborah anticline bendigo victoria australia gold mineralization along the deborah anticline bendigo australia occurs in quartz veins that are categorized into two main groups those associated with folds and those associated with faults the relative chronology of the structural development and quartz vein emplacement is characterized by the initial development of the fold and the subsequent formation of bedding and cleavage parallel veins saddle reefs may have developed at this stage reverse faults and their associated veins formed after folds had locked up major gold hosting structures include saddle reefs reverse faults and composite fold fault structures where reverse faults have disrupted saddle reefs some reverse faults are interpreted to have propagated along preexisting structures such as bedding parallel veins although gold is hosted in fold related structures the majority is found in veins associated with later faults folds and fold related veins strongly controlled the location of these later formed reverse faults and their associated veins a fault based fracture system was superimposed on preexisting dilational sites such as bedding parallel veins and saddle reefs and it is possible that this allowed for the introduction of a larger volume of fluids during faulting than was possible during folding

the effects of stress and fracturing on permeability of coal abstract this paper examines the changes in structure and permeability of coal under the stress conditions experienced around longwall faces the effect of fracturing on permeability of coal is discussed and the stress permeability relationship for fractured coal is compared with that of non fractured coal an empirical relationship between stress and permeability for coal is derived from the experimental data which relates the stress permeability behaviour of coal to its rank through the compressibility of the coal itself

ventilation rates of the waters in the nansen basin of the arctic ocean derived from a multitracer approach tritium sup 3 he sup 14 c and helium neon data from a station located in the central nansen basin of the arctic ocean are reported and discussed it is demonstrated that sup 3 he is a valuable tracer for studies of the upper water column and together with tritium sup 3 he provides a rough time scale of the ventilation of these waters the apparent tritium sup 3 he age is about 7 years in the surface water and about 14 years in the lower part of the halocline water of atlantic origin defined by a temperature maximum shows tritium sup 3 he ages between 7 and 9 years this variation of ages indicates that the circulation of the individual water layers of the upper water column is largely decoupled and occurs on different time scales tritium sup 3 he ages observed in the arctic intermediate water suggest a ventilation on a time scale of 15 to 20 years depth 1 000 m the mean age of the eurasian basin bottom water is estimated on the basis of sup 14 c data to approximately 200 to 250 years there is no indication of noble gas fractionation due to sea ice formation below the surface layer from analysis of the sup 3 he backgroundmore it appears that there is a small primordial sup 3 he component in eurasian basin bottom water less

internal kinematics of salt diapirs the internal structure of intrusive and extrusive salt bodies elucidates their external shape and the mechanism and history of diapiric emplacement information relevant to petroleum exploration trace amounts of brine can act like heat to weaken salt and promote geologic creep by solution transfer mechanisms we compare natural strain markers in salt with the artificial markers used by fluid dynamicists stream lines are the smooth flow paths followed by fluid particles stream surfaces separate flow laminae and contain the stream lines grain shape fabrics in salt anneal readily and have strain memories so short that lineations map the stream lines and foliations map the stream surfaces of the last stages of deformation by contrast larger structures like folded beddi g have much longer strain memories as a result multiple generations of tonguelike recumbent flow folds formed by unsteady flow in the mother source layer rotate to upright sheath folds or spines in the stems of diapirs here they are constricted and refolded into steep curtain folds to form crescentic and other interference patterns visible in the roofs of salt mines mature diapirs can form crestal bulbs which may be balloon or mushroom shaped and which potentially form larger petroleum traps than previously supposed screens of country rock may be entrained between the stem and peripheral overhanging lobes caused by episodic sedimentation

insights into the mechanics of en echelon sigmoidal vein formation using ultra high resolution photogrammetry and computed tomography abstract two novel techniques photo based reconstruction photogrammetry and computed tomography ct are used to investigate the formation of an exceptional array of sigmoidal veins in a hand sample from cape liptrap southern victoria and to provide constraint on models for their development the accuracies of the photogrammetric models were tested by comparison with a laser scan generated three dimensional 3d model the photogrammetric model was found to be accurate to at least 0 25 mm and substantially more detailed than the laser scan a methodology was developed by which 3d structural measurements could be extracted from the photogrammetric model this was augmented with the ct model which through its capacity to elucidate internal structure was used to constrain the geometry and linkage of structures within the rock volume the photogrammetric and ct data were then combined with detailed photomicrographs to evaluate the evolution of the sigmoidal veins in the sample the angle between the sigmoidal vein margins and an inferred shear zone as well as the orientations of the crystal fibres were found to imply a rotation of 27 however coeval pressure solution seams and older veinlets in the rock bridges between the veins were only found to have rotated by 10 an observation not easily explained using existing models for sigmoidal vein formation a new model is proposed in which a significant component of sigmoidal vein geometry is due to localised dilation caused by slip on the pressure solution seams the process involves strain partitioning onto pressure solution seams which leads to exaggeration of sigmoidal vein geometries if not accounted for the apparent vein rotation due to slip partitioning introduces errors into calculations of simple shear and volume strain based on sigmoidal arrays of this type furthermore the ct data demonstrated that in 3d the veins are continuous and channel like implying a far higher degree of connectivity and fluid transport than is suggested by their 2d form

on the role of interior mixing and air sea fluxes in determining the stratification and circulation of the oceans abstract the problem of determining the eastern boundary basic stratification and the buoyancy driven circulation of the oceans is addressed a global integral constraint relating the interior stratification and the air sea heat fluxes is derived based on the condition that the total mass of water of given density is constant in a steady state ocean this constraint is then applied to two simple analytic models the first is a continuous nonlinear diffusive model of the lower mid depth and bottom circulation below the influence of the wind driven circulation it shows the tendency of the vertical density profile to look like an exponential profile in the presence of mixing the integral constraint is used to relate the stratification and circulation of the bottom and mid depth waters to the air sea heat fluxes at the surface where the deep densities outcrop the second model is a layered one of the wind driven circulation mid depth and bottom water the eastern boundary stratification of the model i

origin and composition of seasonal labrador sea freshwater the depth of winter convection in the central labrador sea is strongly influenced by the prevailing stratification in late summer for this late summer stratification salinity is as important as temperature and in the upper water layers salinity even dominates to analyze the source of the spring and summer freshening in the central region seasonal freshwater cycles have been constructed for the interior labrador sea the west greenland current and the labrador current it is shown that none of the local freshwater sources is responsible for the spring summer freshening in the interior which appears to occur in two separate events in april to may and july to september comparing the timing and volume estimates of the seasonal freshwater cycles of the boundary currents with the central labrador sea helps in understanding the origin of the interior freshwater signals the first smaller pulse cannot be attributed clearly to either of the boundary currents the second one is about three times stronger and supplies 60 of the seasonal summer freshwater transport estimates and calculated mixing properties provide evidence that its source is the west greenland current the finding implies a connection also on interannual time scales between labrador sea surface salinity and freshwater sources in the west greenland current and farther upstream in the east greenland current the freshwater input from the west greenland current thus also is the likely pathway for the known modulation of labrador sea water mass formation by freshwater export from the arctic via the east greenland current which implies some predictability on longer time scales

how is the ocean filled 1 the ocean surface rapidly exchanges heat freshwater and gases with the atmosphere but once water sinks into the ocean interior the inherited properties of seawater are closely conserved previous water mass decompositions have described the oceanic interior as being filled by just a few different property combinations or water masses here we apply a new inversion technique to climatological tracer distributions to find the pathways by which the ocean is filled from over 10 000 surface regions based on the discretization of the ocean surface at 2 by 2 resolution the volume of water originating from each surface location is quantified in a global framework and can be summarized by the estimate that 15 of the surface area fills 85 of the ocean interior volume ranked from largest to smallest the volume contributions scaled by surface area follow a power law distribution with an exponent of 1 09 0 03 that appears indicative of the advective diffusive filling characteristics of the ocean circulation as demonstrated using a simple model this work quantifies the connection between the surface and interior ocean allowing insight into ocean composition atmosphere ocean interaction and the transient response of the ocean to a changing climate

transit time and tracer age distributions in geophysical flows transport in the atmosphere and in the ocean is the result of the complex action of time dependent and often highly turbulent flow a useful diagnostic that summarizes the rate at which fluid elements are transported from some region to a point or the reverse via a multiplicity of pathways and mechanisms is the probability density function pdf of transit times the first moment of this pdf often referred to as mean age has become an important transport diagnostic commonly used by the observational community this paper explores how to probe the flow with passive tracers to extract transit time pdf s as a foundation the literal tracer age is defined as the elapsed time since tracer was injected into the flow and the corresponding tracer age distribution z as the fractional tracer mass in a given interval of tracer age the distribution z has concrete physical interpretation for arbitrary sources but is only equivalent to a tracer independent transit time pdf of the flow in special cases the transit time pdf is a propagator g9 of boundary conditions the age spectrum of t m hall and r a plumb applied over a control surface v the propagator g9 is shown to be the flux into v resulting from a unit mass injected into the time reversed flow through explicit construction of the transit time pdf using the concept of tracer age the special cases for which z and g9 coincide are established this allows a direct physical demonstration of g9 and its adjoint g9 as the pdf s of transit times since fluid at point r had last contact with v and until fluid at r will have first contact with v respectively in the limit as v is shrunk to a point point to point transit time pdf s are well defined but their mean transit time and higher order moments become infinite several concrete geophysical examples are considered to illustrate under what conditions characteristics of tracer age and transit time pdf s can be inferred from observations in the atmosphere or the ocean

spatial distribution of ore deposits conventional spatial distributions such as the negative binomial and neyman scott have been proposed as models for the clustered distribution of ore deposits b b mandelbrot has proposed that ore deposits are clustered at many different scales and that fractal distributions are appropriate the apparent fractal characteristics of geologic controls on the locations of hydrothermal deposits self similar systems of fractures circulation cells and magmatic intrusions support his proposal examination of the spatial distribution of 4775 hydrothermal precious metal deposits in the basin and range western united states reveals fractal distributions acting within two scale ranges together covering the entire range from 1 to 1000 km this result gives additional credibility to concepts of regional controls on mineralization such as metallogenic provinces and tectonostratigraphic terranes the distribution of these ore deposits about a known occurrence follows a regular radial density law within a range of radii r of 1 to 15 km the probability density function of these deposits is given by d 0 46 r 1 17 and within a range of radii of 15 to 1000 km by d 0 08 r 0 83 where d is deposits per square kilometre

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

hydrography of the labrador sea during active convection the hydrographic structure of the labrador sea during wintertime convection is described the cruise part of the deep convection experiment took place in february march 1997 amidst an extended period of strong forcing in an otherwise moderate winter because the water column was preconditioned by previous strong winters the limited forcing was enough to cause convection to approximately 1500 m the change in heat storage along a transbasin section relative to an occupation done the previous october gives an average heat loss that is consistent with calibrated national centers for environmental prediction surface heat fluxes over that time period 200 wm 22 deep overturning was observed both seaward of the western continental slope which was expected as well as within the western boundary current itself something that had not been directly observed previously these two geographical regions separated by roughly the 3000 m isobath produce separate water mass products the offshore water mass is the familiar cold fresh dense classical labrador sea water lsw the boundary current water mass is a somewhat warmer saltier lighter vintage of classical lsw though in the far field it would be difficult to distinguish these products the offshore product was formed within the cyclonic recirculating gyre measured by lavender et al in a region that is limited to the north most likely by an eddy flux of buoyant water from the eastern boundary current the velocity measurements taken during the cruise provide a transport estimate of the boundary current throughput and offshore recirculation finally the overall trends in stratification of the observed mixed layers are described

middepth spreading in the subpolar north atlantic ocean reconciling cfc 11 and float observations 1 chlorofluorocarbons cfcs enter the middepth layers of the north atlantic ocean from the atmosphere during the formation of dense mode water in the labrador and irminger seas of the subpolar gyre the cfc bearing waters then spread from the convection regions through advection and diffusion of the water masses using recent estimates of the circulation at 1500 m depth from subsurface profiling floats the spreading of cfc 11 is simulated in the subpolar north atlantic with an advective diffusive model several numerical experiments are performed with different stream functions lateral diffusivities and variations in the cfc 11 sources the results are then compared to the observed cfc 11 field during 1996 1998 poor fits are found for diffusivities less than about 500 m 2 s 1 better fits are found for diffusivities ranging from 500 12 000 m 2 s 1 although unrealistically smooth model solutions are produced if the diffusivity exceeds about 3000 m 2 s 1 simulations that include both labrador and irminger sea cfc 11 sources fit the data better than with labrador sources alone none of the model cfc solutions fit the data within the cfc uncertainty over the whole domain the model performs well in the western part of the subpolar gyre but cfc 11 concentrations are consistently too low in the west european basin it is possible that uncertainty in the float based circulation can account for these misfits and a more accurate circulation estimate might be able to fit the observed cfc 11 field alternatively time variations in the flow or deep water formation processes which clearly exist in the real ocean may need to be included

the origins of late twentieth century variations in the large scale north atlantic circulation abstractsurface forcing perturbation experiments are examined to identify the key forcing elements associated with late twentieth century interannual to decadal atlantic circulation variability as simulated in an ocean sea ice hindcast configuration of the community earth system model version 1 cesm1 buoyancy forcing accounts for most of the decadal variability in both the atlantic meridional overturning circulation amoc and the subpolar gyre circulation and the key drivers of these basin scale circulation changes are found to be the turbulent buoyancy fluxes evaporation as well as the latent and sensible heat fluxes these three fluxes account for almost all of the decadal amoc variability in the north atlantic even when applied only over the labrador sea region year to year changes in surface momentum forcing explain most of the interannual amoc variability at all latitudes as well as most of the decadal variability south of the equator the observed strengthening of southern ocean westerly wi

groundwater flow along and across structural folding an example from the judean desert israel abstract the considerable influence of the geological structure on groundwater flow regime is exhibited in the thick carbonate aquifer beneath the judean desert israel groundwater flow is diverted from the general steep hydraulic gradient creating a subsurface river like meandering flow pattern the structure of the extensive folded anticlinorium forces groundwater flow through synclinal axes in the upper aquifer and in places it overflows from one to an adjacent syncline groundwater outflows are at tsukim kane samar and en gedi springs near the dead sea shore and by sub surface flow across the graben faults towards the dead sea in this study all available data are integrated and processed first ever to form a complete representation of the three dimensional hydrostratigraphy and hydrogeology using numerical modeling modflow we analyzed quantitatively the flow regime leakage rates between upper and lower sub aquifers and between adjacent sub basins the groundwater mass balance and aquifer hydraulic properties this study has practical implications regarding recent groundwater management future possibilities of groundwater development for the benefit of both israelis and palestinians residing in the area and conservation of nature reserves located along the dead sea

rates and mechanisms of water mass transformation in the labrador sea as inferred from tracer observations time series of hydrographic and transient tracer 3h and 3he observations from the central labrador sea collected between 1991 and 1996 are presented to document the complex changes in the tracer fields as a result of variations in convective activity during the 1990s between 1991 and 1993 as atmospheric forcing intensified convection penetrated to progressively increasing depths reaching 2300 m in the winter of 1993 over that period the potential temperature salinity s properties of labrador sea water stayed nearly constant as surface cooling and downward mixing of freshwater was balanced by excavating and upward mixing of the warmer and saltier northeast atlantic deep water it is shown that the net change in heat content of the water column 150 2500 m between 1991 and 1993 was negligible compared to the estimated mean heat loss over that period 110 w m 2 implying that the lateral convergence of heat into the central labrador sea nearly balances the atmospheric cooling on a surprisingly short timescale interestingly the 3h 3he age of labrador sea water increased during this period of intensifying convection starting in 1995 winters were milder and convection was restricted to the upper 800 m between 1994 and 1996 the evolution of 3h 3he age is similar to that of a stagnant water body in contrast the increase in and s over that period implies exchange of tracers with the boundaries via both an eddy induced overturning circulation and along isopycnal stirring by eddies with an exchange coefficient of o 500 m2 s 1 the authors construct a freshwater budget for the labrador sea and quantitatively demonstrate that sea ice meltwater is the dominant cause of the large annual cycle of salinity in the labrador sea both on the shelf and the interior it is shown that the transport of freshwater by eddies into the central labrador sea 140 cm between march and september can readily account for the observed seasonal freshening finally the authors discuss the role of the eddy induced overturning circulation with regard to transport and dispersal of the newly ventilated labrador sea water to the boundary current system and compare its strength 2 3 sv to the diagnosed buoyancy forced formation rate of labrador sea water

fractal models for ore reserve estimation abstract traditional geometric and geostatistic methods for reserve estimation in a single deposit are difficult to use with skewed distribution mineralization variables including grade orebody thickness and grade thickness a common characteristic of most deposits and require complex data processing it has been shown that the skewed mineralization variables can be described by the number size model in a fractal domain based on the number size model assuming that orebody thickness and grade thickness are continuous variables the fractal model for reserve estimation fmre in a single deposit can be established in the fmre ore tonnage can be estimated given the orebody area and the fractal parameters of orebody thickness distribution and metal tonnage can be estimated based on the orebody area and the fractal parameters of grade thickness distribution the reserve estimated by the fmre can denote actual ore tonnage and metal tonnage that can be mined out of the deposit the frme was applied to the dayingezhuang gold deposit in the jiaodong gold province in china the gold reserves via the fmre and the traditional geometric block method are similar with relative errors of 3 11 in ore tonnage and 0 29 in metal tonnage compared to traditional reserve estimation the fmre is much easier in calculation process and is more reasonable in dealing with the skewed distribution however this new method fails to calculate local reserve which can be derived via any of the traditional estimation methods

control and prevention of gas outbursts in coal mines riosa olloniego coalfield spain abstract underground coal mines have always had to control the presence of different gases in the mining environment among these gases methane is the most important one since it is inherent to coal despite of the technical developments in recent decades methane hazards have not yet been fully avoided this is partly due to the increasing depths of modern mines where methane emissions are higher and also to other mining related circumstances such as the increase in production rates and its consequences difficulties in controlling the increasing methane levels increasing mechanization the use of explosives and not paying close attention to methane control systems the main purposes of this paper are to establish site measurements using some critical parameters that are not part of the standard mining control methods for risk assessment and to analyze the gas behavior of subvertical coal seams in deep mines in order to prevent gas incidents from occurring the ultimate goal is the improvement in mining conditions and therefore in safety conditions for this purpose two different mines were instrumented for mine control and monitoring both mines belong to the riosa olloniego coalfield in the asturias central basin spain and the areas instrumented are mined via subhorizontal sublevels at an actual depth of around 1000 m under the overburden of mount lusorio during this research a property favoring gas outbursts was site measured for the first time in an outburst prone coal 8th coalbed gas pressure and its variations which contributed to complete the data available from previous characterizations and to set some guidelines for assessing the potential outburst prone areas a gas measurement tube set has been designed for measuring gas pressure as well as its variation over time as a result of nearby workings and to calculate permeability the paper establishes the effect of overlapping of works but it also shows the efficacy of two preventive measures to be applied high pressure water infusion and the exploitation of a protective coal seam 7th coalbed that must be mined preferably two complete sublevels before commencing the advance in the outburst prone coalbed both measures constitute an improvement in the mining sequence and therefore in safety and should be completed with a systematic measurement to control the risk gas pressure in the 8th coalbed in the area of influence of other workings to establish the most suitable moment to renew the advance further researches could focus on ascertaining the permeability not only in mined areas but also in areas of the mine that are still not affected by mining work and on tuning more finely the ranges of influence of overstress time and overlap distance of the workings of the 7th coalbed in the 8th coalbed

observations of the labrador sea eddy field this paper is an observational study of small scale coherent eddies in the labrador sea a region of dense water formation thought to be of considerable importance to the north atlantic overturning circulation numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat yet their small size has hindered observational progress a large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms current meter moorings and satellite altimetry details of the current and water mass structure of individual eddy events as they are swept past by an advecting flow can then be extracted from the mooring data a transition is seen during mid 1997 with long lived boundary current eddies dominating the central labrador sea year round after this time and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time the topex poseidon altimeter covers the labrador sea with a loose net of observations through which coherent eddies can seem to appear and disappear by concentrating on locating and describing anomalous events in individual altimeter tracks a portrait of the spatial and temporal variability of the underlying eddy field can be constructed the altimeter results reveal an annual pulsation of energy and of coherent eddies originating during the late fall at a particular location in the boundary current pinpointing the time and place of the boundary current type eddy formation the interannual variability seen at the mooring is reproduced but the mooring site is found to be within a localized region of greatly enhanced eddy activity notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling these eddy observations as well as hydrographic evidence suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region

information from folds a review abstract folds are spectacular geological structures that are seen in layered rock on many different scales to mark 30 years of the journal of structural geology we review the information that can be gained from studies of folds in theory experiment and nature we first review theoretical considerations and modeling from classical approaches to current developments the subject is dominated by single layer fold theory with the assumption of perfect layer parallel shortening but we also review multilayer fold theory and modeling and folding of layers that are oblique to principal stresses and strains this work demonstrates that viscosity ratio degree of non linearity of the flow law anisotropy and the thickness and spacing distribution of layers of different competence are all important in determining the nature and strength of the folding instability theory and modeling provide the basis for obtaining rheological information from natural folds through analysis of wavelength thickness ratios of single layer folds and fold shapes they also provide a basis for estimating the bulk strain from folded layers information about folding mechanisms can be obtained by analysis of cleavage and fabric patterns in folded rocks and the history of deformation can be revealed by understanding how asymmetry can develop in folds by how folds develop in shear zones and how folds develop in more complex three dimensional deformations

the impact of a bottom boundary layer scheme on the north atlantic ocean in a global coupled climate model abstract although the overflow and descent of cold dense water across the greenland iceland scotland ridge is the principal means for the maintenance of the thermohaline circulation in the north atlantic ocean this feature is not adequately treated in global ocean numerical models in this paper a bottom boundary layer scheme is introduced into the hadcm3 coupled atmosphere ocean sea ice general circulation climate model in order to give an improved representation of cold water formation in the north atlantic ocean the scheme uses a simple terrain following bottom boundary layer incorporated into the ocean general circulation model only the tracer tendencies are evaluated in the bottom boundary layer with the velocities taken from the near bottom interior values it is found that with the bottom boundary layer scheme there are several significant effects on the deep water formation and flow the overflow of dense water from the nordic seas into the north atlantic seas is improved with the introduc

an estimate of the eddy induced circulation in the labrador sea regions of oceanic deep convection such as the labrador sea are prone to baroclinic instability the resulting geostrophic eddies play a crucial role in the post convection adjustment process which involves both rearrangement of mass so as to release available potential energy and exchange of heat and salt with the boundaries in this study it is proposed that the slumping of isopycnals associated with baroclinic instability drives an eddy induced overturning circulation consisting of a surface intensified flow transporting low salinity water from the boundary currents into the interior sinking motion in the interior and an outflow at depth transporting newly ventilated labrador sea water towards the boundaries typical eddy induced velocities estimated from hydrographic data are roughly 0 5 cm s for the surface inflow 1 m day for the vertical motion and 0 1 cm s for the deeper outflow in close agreement with those calculated in a numerical model

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

oceanic transport of surface meltwater from the southern greenland ice sheet meltwater runoff from the greenland ice sheet alters ocean surface salinity numerical simulations show that meltwater from southeastern greenland is transported to the labrador sea more efficiently than that from southwestern greenland

a fractal approach to the relationship between ore grade and tonnage it is now recognized that a variety of natural processes exhibit scale invariance over a wide range of scales scale invariant processes often exhibit a fractal behavior there are various ways to define fractal behavior one is to relate the frequency of occurrence to size tonnage and grade relations for economic ore deposits exhibit a fractal behavior if the tonnage of ore with a mean grade is proportional to the mean grade raised to a power we show that such a relation is a good approximation for mercury copper and uranium deposits in the united states the respective fractal dimensions are 2 01 1 16 and 1 48 the renormalization group approach is a quantitative method for studying scale invariant processes if it is assumed that the concentration of elements in ores is statistically scale invariant the renormalization group approach can be used to derive a fractal relationship between tonnage and mean grade

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

freshwater sources to the coastal ocean off northeastern north america evidence from h2 18o h2 16o oxygen isotope h218o h216o salinity data identify freshwater sources along the northeastern north american continental margin the oxygen isotope 18o salinity s properties of various water types are distinguished sea ice formation on the labrador shelf is shown to influence 18o s values it is estimated that 2 3 m of freshwater is extracted from the water column to form sea ice it is hypothesized that waters on the scotian shelf gulf of maine and the middle atlantic bight are composed of slope water diluted by an upstream low salinity source this upstream source is a mixture of brine enriched labrador shelf water and st lawrence river water the 18o value of the apparent freshwater component 18os 0 of waters on the scotian shelf and farther south is 20 which has been used to suggest a sole high latitude freshwater source we show instead that the st lawrence river contributes 35 of the freshwater on the scotian shelf in agreement with the physical oceanographic evidence the remaining freshwater is supplied by high latitude rivers dominated by arctic runoff finally the isotope evidence identifies baffin bay as an important pathway by which freshwater from the arctic ocean can reach the labrador sea

controls on mineral deposit occurrence inferred from analysis of their spatial pattern and spatial association with geological features in this paper point pattern analysis fractal analysis and fry analysis were employed to study the spatial pattern of known occurrences of mineral deposits of the type sought whereas distance distribution method was applied to study the spatial associations between various geological features and known occurrences of mineral deposits of the type sought in the aroroy district philippines the results of the applications of these spatial analytical techniques support a conceptual model of district scale mechanism of geologic controls on low sulphidation epithermal au mineralization which involves a more or less regular mesh of interlinked zones of extension faults fractures at and or around intersections of nnw and nw trending strike slip faults fractures integration of spatial evidential data layers representing these structural controls and surficial geochemical anomalies via knowledge guided application of data driven evidential belief functions results in delineation of prospective areas occupying about 25 of the district in which there is about 70 likelihood of undiscovered occurrences of low sulphidation epithermal au deposits

acoustic emission and thermal infrared precursors associated with bump prone coal failure abstract coal bump is sudden catastrophic failure of coal and usually causes serious problems to underground coal mining the acoustic and thermal infrared radiation tir characteristics of bump prone coal under uniaxial compression and cyclic loading conditions are investigated in this study the monitoring system consists of a tir observation system a stress and strain measurement system and an acoustic emission monitoring system precursory information for impending failure of coal samples is collected including tir acoustic emission and strain precursors moreover the response speed and the sensitivity of different monitoring systems during the cracking events in the samples are studied under different loading conditions the microstructure of coal sample is analyzed by x ray computerized tomography ct and scanning electron microscope sem the experiment results show that 0 9 c c is the compressive strength and 0 82 c can be regarded as the stress caution points for the failure of bump prone coal under uniaxial compression and under uniaxial cyclic compression respectively they are much higher than 0 79 c as the stress caution point for the normal coal samples it is also indicated that the temperature at coal surface or in the coal mass should be monitored at the perimeter of the site with anticipated collapses it can be a valuable tool to obtain the precursors for mine disaster control such as coal bumps gas outburst and water inrush

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

on mapping the diapycnal water mass transformation of the upper north atlantic ocean abstractdiapycnal water mass transformation is the essence behind the atlantic meridional overturning circulation amoc and the associated heat freshwater transports existing studies have mostly

propagation of tracer signals in boundary currents abstract the propagation of a range of tracer signals in a simple model of the deep western boundary current is examined analytical expressions are derived in certain limits for the transit time distributions and the propagation times tracer ages of tracers with exponentially growing or periodic concentration histories at the boundary current s origin if mixing between the boundary current and the surrounding ocean is either very slow or very rapid then all tracer signals propagate at the same rate in contrast for intermediate mixing rates tracer ages generally depend on the history of the tracer variations at the origin and range from the advective time along the current to the much larger mean age close agreement of the model with chlorofluorocarbon cfc and tritium observations in the north atlantic deep western boundary current dwbc is obtained when the model is in the intermediate mixing regime with current speed around 5 cm s 1 and mixing time scale around 1 yr in this regime anomalies

performance of a second order moments advection scheme in an ocean general circulation model 1 the reliability of ocean general circulation models ogcms strongly depends on the quality of their tracer advection schemes for the sake of simplicity and computing time tracer advection schemes most commonly used in large scale ogcms tend to be low order schemes which suffer from spurious numerical diffusion and dispersion that result in distorted solutions the application of high order schemes would reduce numerical errors but at a considerable cost in terms of computing time an alternative to the use of high order methods is the implementation of algorithms that take into account the sub grid distribution of tracers one such method is the second order moments som scheme of prather 1986 which is more accurate than a fourth order scheme but at the time consumption of a second order algorithm this article presents results from coarse resolution global ocean simulations with very low explicit diapycnal mixing in which active and passive tracers were advected with the som method we compare the performance of the method with that of more traditional schemes namely the fct flux corrected transport and quicker quadratic upstream interpolation for convective kinematics schemes in general the use of the som method significantly improves tracer distributions and transports compared to fct and quicker thus leading to a better representation of ocean currents notably boundary currents and frontal systems while model simulations employing the fct and quicker schemes recreate a global overturning circulation with strong upwelling occurring in low latitudes the som simulations admit a circulation pattern closer to that known as the reconfigured conveyor belt toggweiler and samuels 1993 in which the bulk of the global ocean upwelling occurs in the southern ocean

stochastic stability of open ocean deep convection open ocean deep convection is a highly variable and strongly nonlinear process that plays an essential role in the global ocean circulation a new view of its stability is presented here in which variability as parameterized by stochastic forcing is central the use of an idealized deep convection box model allows analytical solutions and straightforward conceptual understanding while retaining the main features of deep convection dynamics in contrast to the generally abrupt stability changes in deterministic systems measures of stochastic stability change smoothly in response to varying forcing parameters these stochastic stability measures depend chiefly on the residence times of the system in different regions of phase space which need not contain a stable steady state in the deterministic sense deep convection can occur frequently even for parameter ranges in which it is deterministically unstable this effect is denoted wandering unimodality the stochastic stability concepts are readily applied to other components of the climate system the results highlight the need to take climate variability into account when analyzing the stability of a climate state