a cool anomaly off northern california an investigation using ir imagery and in situ data satellite ir imagery and in situ hydrographie data are used to understand better the mesoscale variability of the california current system and to explore the relation of its surface and subsurface thermal structures in august 1982 one of the cool filaments commonly seen in satellite ir images during summer off northern california was sampled hydrographically during an optoma ocean prediction through observation modeling and analysis cruise based on the cool anomaly seen in a series of ir images and the in situ hydrographie data and based on geostrophic calculations a jet entrained upwelled coastal water and advected it rapidly through the warmer waters offshore providing an important cross shore transfer process the anomaly was about 50 km wide and extended vertically to about 40 m the temperature patterns at the surface were well correlated with those to about 30 m below 50 m the surface temperature was better correlated with horizontal temperature gradients i e the thermal wind consistent with strong horizontal advection by the geostrophic jet the cool anomaly was also relatively dense based on investigation of the t s properties the coastal water had been diluted through mixing with columbia river plume water on the northern edge of the anomaly near the temperature front in the shoreward sampled portion of the anomaly and just south of the anomaly interleaving occurred there was also a surface saline anomaly embedded in the cool anomaly near the temperature front the location of the temperature front in the in situ data and in the ir imagery corresponded well the temperature front was tracked in a series of ir images over 2 weeks the reorientation of the seaward extremity of the anomaly from westward to northwestward and the southwestward displacement of its southern boundary at speeds of 2 to 5 km d were consistent with the propagation of mesoscale features evident in successive quasi synoptic surface dynamic topography maps the southwestward displacement was probably also related to surface ekman transport

paleomagnetism of jurassic radiolarian chert above the coast range ophiolite at stanley mountain california and implications for its paleogeographic origins upper jurassic red tuffaceous chert above the coast range ophiolite at stanley mountain california lat 35 n long 240 e contains three components of remanent magnetization the first component a removed by 100 200 c has a direction near the present day field for southern california and is probably a recently acquired thermoviscous magnetization a second component b removed between 100 and 600 c is identical to that observed by previous workers in samples of underlying pillow basalt and overlying terrigenous sedimentary rocks this component has constant normal polarity and direction throughout the entire section although these rocks were deposited during a mixed polarity interval of the geomagnetic field the b magnetization therefore is inferred to be a secondary magnetization acquired during accretion uplift or miocene volcanism prior to regional clockwise rotation the highest temperature component c removed between 480 and 680 c is of dual polarity and is tentatively interpreted as a primary magnetization although it fails a reversal test possibly due to contamination by b separation of the b and c components is best shown by samples with negative inclination c directions and a corrected mean direction using only these samples indicates an initial paleolatitude of 32 n 8 paleobiogeographic models relating radiolarian faunal distribution patterns to paleolatitude have apparently been incorrectly calibrated using the overprint b component few other paleomagnetic data have been incorporated in these models and faunal distribution patterns are poorly known and mostly unquantified the available data therefore do not support formation of the coast range ophiolite at stanley mountain near the paleoequator or accretion at 10 n paleolatitude as has been previously suggested based on paleomagnetic data but indicate deposition near expected paleolatitudes for north america 35 n 4 during late jurassic time

relative dispersion of surface drifters in the benguela upwelling region abstractwe examine the relative dispersion of surface drifters deployed in groups of triplets at the boundaries of a filament in the upwelling region off namibia for both the entire ensemble and th

physical description of an upwelling filament west of cape st vincent in late october 2004 1 the present paper describes the physical characteristics of an upwelling filament off cape st vincent southern iberia in october 2004 based on remote sensing hydrographic adcp and wind data it was associated with a meandering jet similar to eastern pacific or canary filaments though its dynamical features were weaker as a result of the surface trapped top 100 m and weak horizontal density gradients the filament transported 0 9 sv of coastal water offshore of which 8 was due to ekman transport it formed following the destabilization of an alongshore equatorward upwelling jet close to the cape the filament was structurally asymmetric with anticyclonic geostrophic vorticity to the north and more strongly cyclonic to the south as a result of the meanders and existing eddies the filament comprised a sequence of cold submesoscale 30 km diameter cyclones vertical velocities of 15 m d 1 were associated with meanders of the jet the surface and subsurface circulation was coupled at middepths 90 150 m anticyclonic recirculation of northern water seemed associated with a separated older upwelling jet mediterranean water mw was present below 350 dbar as a topographically steered undercurrent and a meddy cyclone dipole these undercurrents contributed to the formation of the october filament through baroclinic instability associated with the enhanced vertical shear

timing of colorado plateau uplift initial constraints from vesicular basalt derived paleoelevations we have developed a technique for measuring paleoelevation on the basis of the vesicularity of basaltic lava flows we are currently applying this technique to determine the timing and extent of cenozoic uplift of the colorado plateau because the technique measures paleoatmospheric pressure it is not subject to uncertainties stemming from the use of proxies that depend on environmental factors other than elevation alone vesicular lavas preserve a record of paleopressure at the time and place of lava emplacement because the difference in internal pressure in bubbles at the base and top of a lava flow depends on atmospheric pressure and lava flow thickness the modal size of the vesicle bubble population is larger at the top than at the bottom this leads directly to paleoatmospheric pressure and thus elevation because the thickness of the flow can easily be measured in the field and the vesicle sizes can be measured in the laboratory on the colorado plateau volcanic fields are generally found around the margins of the plateau basaltic lavas range in age from 0 to 23 ma present elevations range from 1 7 km to 3 3 km samples were collected from lava flows in the areas of marysvale springerville grand mesa and the san juan mountains and analyzed to determine the timing and extent of uplift the analysis of the samples using x ray computed tomography imaging and our numerical techniques for determining vesicle population statistics indicate uplift of 350 2200 m depending on age there is a clear relationship between age and amount of uplift original elevation subtracted from present elevation the results indicate slow uplift of 40 m m y between 25 ma and 5 ma only 800 m of uplift during that time and rapid uplift of 220 m m y since 5 ma 1100 m during that time these results reconcile the long standing controversy between interpretations of ancient versus recent uplift by providing an uplift history curve for the colorado plateau

high resolution x ray computed tomography of impactites 1 high resolution x ray computed tomography hrxct is a nondestructive method used to study the interiors of opaque solid objects here we present the results of a first application of the hrxct method to imaging the interior of impactites in particular suevites glass bearing impact breccias from the bosumtwi ghana and ries germany craters and a muong nong type tektite from thailand the aim of these studies was to determine the three dimensional 3 d distribution of clasts within the matrix of the suevites to test this technique with respect to its suitability for the recognition of different clast types of different densities and to determine textural characteristics of the tektite the main part of the study concentrated on a large suevite sample about 10 7 5 cm from the bosumtwi impact structure target rock fragments in the bosumtwi sample consist of greywacke and sandstone quartzitic rocks shale and phyllite and granites another large clast component is composed of impact melt and glass fragments macroscopic petrography and thin section petrography were used to identify the clast types in the specimen for correlation with its hrxct signatures the results show that hrxct allows the easy discrimination of the relatively frothy inclusions of glassy melt in the suevites as they are darker than the matrix in the raw x ray scans and can be traced through the whole sample color or gray scale applications allow the distinction of at least four different clast types based on density differences the size of the smallest discernable clasts about 0 5 mm is determined by the resolution of the measurements which in turn is a function of scan slice thickness and field of view in the case of the tektite sample we were also able to image the 3 d distribution of vesicles possibly indicating glass flow the hrxct method allows us to determine the three dimensional distribution of clast populations in impact breccias by image processing techniques and to quantify their abundances in volume percent

ct derived porosity distribution and flow domains computed x ray tomography images of dry undisturbed soil samples of the coarse sandy loam of korkusova hut kh and the fine sand of hupselse beek hb are analysed concerning the image resolution the direction of scanning and the evaluation of boundaries between the fast and slow flow domains the image resolution appears to be a less important factor than the direction of scanning additional data sets are recommended for partitioning the fast and slow flow domains comparison is made with the tracer breakthrough pictures magnetic resonance mr images and outflow volumes obtained from infiltration outflow experiments the two soils under study appeared to have essentially different flow dynamics in the kh sandy loam soil the fast flow occurs in regions of high local porosity in case of the hb fine sand the sample appeared to consist of a dense part where the flow process took place and a more porous part which stayed dry flow instability was detected on mr images for the kh soil

getting the inside story using computed x ray tomography to study inclusion trails in garnet porphyroblasts this study demonstrates how high resolution x ray computed tomography can be used to determine the geometry of curved inclusion trails in garnet porphyroblasts for the first time the three dimensional geometry of these features is shown as an animation a stereo pair a vrml model and two dimensional sections the spatial resolution of the data in this study approximately 10 m is high enough to resolve inclusions and finer resolutions are possible comparisons of scan imagery with thin section and microprobe data demonstrate that many typical inclusion phases in garnet porphyroblasts can be clearly distinguished including quartz ilmenite and monazite a sodium metatungstate solution with a density of 1 19 g cm3 was used for a wedge calibration during scanning reducing artifacts to a minimum and allowing maximum image contrast the overall conclusion of this study is that high resolution x ray computed tomography is a quick non destructive technique that is invaluable in the study of porphyroblast microstructure the three dimensional data generated by this technique can be compared with geometries predicted by the varying theoretical models for the formation of curved inclusion trails in garnet porphyroblasts they can also be analyzed to determine the three dimensional orientation of curvature axes in individual porphyroblasts which has not been possible until now

variability in satellite winds over the benguela upwelling system during 1999 2000 1 wind stress variability over the benguela upwelling system is considered using 16 months 01 august 1999 to 29 november 2000 of satellite derived quikscat wind data variability is investigated using a type of artificial neural network the self organizing map som and a wavelet analysis the som and wavelet analysis are applied to an extracted data set to find that the system may be divided into six discrete wind regimes the wavelet power spectra for these wind regions span a range of frequencies from 4 to 64 days with each region appearing to contain distinct periodicities to the north 10 23 5 s the majority of the power occurs during austral winter with a 4 16 day periodicity further investigation of national centers for environmental prediction reanalysis outgoing longwave radiation data indicates that the winter intensification of wind stress off the angolan coast is linked with convective activity over equatorial west africa the summer activity appears to be linked with the intensification of the angolan heat low convective activity over the congo basin appears to impact upon wind stress variability off the angolan coast throughout the year farther south 24 35 s the majority of the power occurs in the summer here a bimodal distribution occurs with peaks of 4 12 and 25 50 days the southernmost regions appear to be forced at higher frequencies by both midlatitude cyclones austral winter and mesoscale coastal lows austral summer at lower frequencies eastward propagating periodic wind events that originate over eastern south america appear to be important to the forcing of wind stress over the southern benguela

three dimensional imaging of earth and planetary materials x ray computed tomography neutron computed tomography and magnetic resonance imaging are driving novel scientific advances by enabling rapid non destructive three dimensional examination and analysis of earth and planetary materials discoveries catalyzed by these approaches range across fields from environmental geology to petroleum geology hydrology to soil science paleontology to petrology and geodynamics to meteoritics they have impacted our understanding of hydrocarbon reservoirs contaminant transport climate change co2 sequestration the evolution of life crustal uplift mantle metasomatism planetary differentiation and more three dimensional imaging is likely soon to become an essential component of every investigator s toolkit especially as instruments and facilities emerge that are optimized for increasingly sophisticated geological applications of these techniques and as access to them expands

vertical structure turbulent mixing and fluxes during lagrangian observations of an upwelling filament system off northwest iberia abstract in august 1998 a recurrent filament located near 42 n off galicia was sampled as part of the omex ii project lagrangian and other observations were made on the shelf where the filament arose and offshore in the filament itself under upwelling favourable but fluctuating winds the shelf drift experiment monitored a change from southward to weak northward net flow as the winds decreased to zero shipborne adcp measurements showed that the shelf was supplying decreasing volumes of water to the filament as the wind speeds decreased at the shelf edge the internal tide was larger than can be explained by local forcing and there were many unusually large high frequency internal waves with a quasi sinusoidal form turbulence observations revealed enhanced dissipation rates and vertical eddy diffusion coefficients within the shelf thermocline of order 1 cm 2 s 1 which appeared to be caused by the breaking of internal wave a second lagrangian experiment was executed in the filament some 120 km offshore which again coincided with a period of wind relaxation cross sections revealed a double cold core and that the offshore flow was limited to a thin surface layer substantial onshore flow occurred below 50 m in the centre of the filament while the strongest and deepest offshore flow coincided with its northern boundary turbulent kinetic energy dissipation rate measurements showed very weak mixing below 15 m in the filament core but enhanced mixing at its boundaries four mixed layer drifters released in the filament initially indicated convergence at its southern boundary marked by strong temperature and salinity contrasts after the wind became more favourable for upwelling the drifters accelerated one drifter traced the full extent of the filament while the other three escaped from it and began to circulate cyclonically over 28 days in a 100 km diameter loop back towards their release point although strong mesoscale activity linked the shelf and ocean regimes offshore transport in the filament was weak at the time of the experiment and vertical and horizontal re circulations on a variety of time scales were important there was sufficient vertical mixing in the thermocline to cause it to thicken and draw some heat into the lower layers during the summer months on the shelf the amount of heat involved was too little to have a significant impact on the development of a filament over a typical lifetime of a week

front eddy influence on water column properties phytoplankton community structure and cross shelf exchange of diatom taxa in the shelf slope area off concepcion 36 37 s in eastern boundary current systems ebcss submesoscale to mesocale variability contributes to cross shore exchanges of water properties nutrients and plankton data from a short term summer survey and satellite time series january february 2014 were used to characterize submesoscale variability in oceanographic conditions and phytoplankton distribution across the coastal upwelling and coastal transition zones north of punta lavapie and to explore cross shelf exchanges of diatom taxa a thermo haline front frn 1 flanked by a mesoscale anticyclonic intrathermocline eddy ite 1 or mode water eddy persisted during the study period and the survey was undertaken during a wind relaxation event at the survey time ite 1 contributed to an onshore intrusion of warm oceanic waters southern section and an offshore advection of cold coastal waters northern section with the latter forming a cold high chlorophyll a filament in situ phytoplankton and diatom biomasses were highest at the surface in frn 1 and at the subsurface in ite 1 whereas values in the coastal zone were lower and dominated by smaller cells diatom species typical of the coastal zone and species dominant in oceanic waters were both found in the frn 1 and ite 1 interaction area suggesting that this mixture was the result of both offshore and onshore advection overall front eddy interactions in ebcss could enhance cross shelf exchanges of coastal and oceanic plankton as well as sustain phytoplankton growth in the slope area through localized upward injections of nutrients in the frontal zone combined with ite induced advection and vertical nutrient inputs to the surface layer

permeability and melt flow in simulated and natural partially molten basaltic magmas abstract a lattice boltzmann method is used to calculate grain scale low reynolds number single phase interstitial porous melt flow in two independent igneous microstructures 1 a microstructure simulated using a stochastic algorithm for progressive crystallization and 2 a natural microstructure obtained through x ray computed tomography ct of a partially melted basalt in both cases the error in the calculated flow field due to finite discretization and domain size has been estimated or demonstrated to be insignificant visually the porous melt flow tends to localize into high flux channels especially with increasing crystallinity and this impression is quantitatively confirmed by increasing skewness of the velocity distribution in the direction parallel to the imposed pressure gradient driving the flow a change from uniform to localized melt flow in naturally occurring situations may have a profound effect on the distribution of trace elements and if the melt is reactive the chemical and structural evolution of the igneous microstructure through localized phase change permeabilities of both microstructures are determined from the calculated steady flow field the permeabilities are then fitted to two different correlation models which are based on the rumpf gupte and carman kozeny relations in these models we express permeability as functions of melt fraction and either the mean crystal length or specific surface area extrapolated permeability to higher melt fractions using both correlation models for the partially melted basalt is shown to be within a factor of four of experimentally determined permeability of a similar sample we determine permeability estimates in the relatively unexplored melt fraction range of 30 80 and find consistency with previous work for permeability estimates in the melt fraction range of 20 30

nondestructive high resolution visualization and measurement of anisotropic effective porosity in complex lithologies using high resolution x ray computed tomography abstract new methods are presented that allow high resolution x ray computed tomography hrxct to be utilized for imaging and measuring the effective porosity field of mineralogically complex specimens at resolutions in the 5 100 m range these methods extend previous established approaches by allowing sample displacement between successive imaging runs and eliminating the need for a highly attenuating tracer a highly detailed map of partial porosity can be generated by scanning a sample in a dry state and infiltrated by distilled water and performing a three dimensional alignment of the two data sets this map can then be used to obtain a number of quantitative analyses such as the frequency distribution of partial porosity and directional analysis to infer flow anisotropy it can also be used for petrographic study of the relationship of porosity to evolving mineralogy in a dynamic system these methods are demonstrated on a series of altered volcanic rocks from a deep sea hydrothermal field

nature of diamonds in yakutian eclogites views from eclogite tomography and mineral inclusions in diamonds abstract we have performed dissections of two diamondiferous eclogites ux 1 and u33 1 from the udachnaya kimberlite yakutia in order to understand the nature of diamond formation and the relationship between the diamonds their mineral inclusions and host eclogite minerals diamonds were carefully recovered from each xenolith based upon high resolution x ray tomography images and three dimensional models the nature and physical properties of minerals in direct contact with diamonds were investigated at the time of diamond extraction polished sections of the eclogites were made containing the mould areas of the diamonds to further investigate the chemical compositions of the host minerals and the phases that were in contact with diamonds major and minor element compositions of silicate and sulfide mineral inclusions in diamonds show variations among each other and from those in the host eclogites oxygen isotope compositions of one garnet and five clinopyroxene inclusions in diamonds from another udachnaya eclogite u51 span the entire range recorded for eclogite xenoliths from udachnaya in addition the reported compositions of almost all clinopyroxene inclusions in u51 diamonds exhibit positive eu anomaly this feature together with the oxygen isotopic characteristics is consistent with the well established hypothesis of subduction origin for udachnaya eclogite xenoliths it is intuitive to expect that all eclogite xenoliths in a particular kimberlite should have common heritage at least with respect to their included diamonds however the variation in the composition of multiple inclusions within diamonds and among diamonds from the same eclogite indicates the involvement of complex processes in diamond genesis at least in the eclogite xenoliths from yakutia that we have studied

seasonal variability of alongshore winds and sea surface temperature fronts in eastern boundary current systems seven years of satellite observations 2003 2009 are used to describe variability in sea surface temperature sst fronts and in the alongshore component of ocean winds and to investigate their relations in four eastern boundary current systems ebcs the general patterns of sst frontal activity are remarkably similar in all ebcs with high frontal probabilities along the coast decreasing with distance from the coastline results from empirical orthogonal function decompositions reveal that the seasonal evolution of sst fronts and wind stress are significantly correlated with intensified upwelling favorable winds associated with an increase in frontal probabilities an offshore migration of the region of high frontal activity is observed during the period of upwelling favorable alongshore wind stress in ebcs in all regions the seasonal variability of frontal activity and wind stress is stronger at mid than at low latitudes the width of the region of high frontal activity is relatively broader in the california and benguela current systems and narrower in the canary and humboldt current systems the width of the band of high frontal activity may be influenced by multiple factors including wind forcing flow topography interactions and mesoscale dynamics while seasonal variability in frontal activity in the california current system acts to reinforce or weaken the average pattern they are substantially different in the canary current system where there is little overlap in the areas characterized by persistent and seasonally varying front activity

the near surface dynamics of coastal upwelling abstract an attempt is made to examine some observational and theoretical aspects of upper ocean dynamics in regions of strong coastal upwelling upper ocean is roughly defined as about the upper 10 30 m of the water column for most systems first the basic surface ekman and mixed layers are discussed including some of the modifications due to upwelling next coastal upwelling fronts and their associated circulation are treated finally areas of strongly three dimensional upwelling are classified and discussed horizontal advection of heat and momentum appear to be generally important for the near surface dynamics of coastal upwelling and these phenomena make realistic theoretical treatments especially difficult

finite amplitude evolution of instabilities associated with the coastal upwelling front abstract a primitive equation model is used to study the finite amplitude evolution of instabilities associated with the coastal upwelling front simulations of increasing complexity are examined that represent idealizations of summer conditions off the oregon coast including cases with steady and with time variable wind in a domain with alongshore uniform bathymetry and with time variable wind in a domain with realistic oregon coast bathymetry the numerical results indicate that the fastest growing mode in this system has approximately an 8 10 km alongshore wavelength but that once the disturbances grow to finite amplitude the predominant alongfront scale increases rapidly because of nonlinear effects separation of the total kinetic energy into contributions from the alongshore average flow and perturbation about that average shows that the initial growth of the perturbation kinetic energy is due to potential energy conversion but transfer of energy from the kinetic energy of the alongshore average

evaluation of local porosity changes in limestone samples under triaxial stress field by using x ray computed tomography abstract the character of reservoir rocks is uncertain and variable at the depths where they are subjected to different tectonic forces and pressure changes due to drilling well stimulation and production operations the stress and time dependent deformation of the porous structure is expected to change the behaviour of the most important properties of the rock such as porosity and permeability which in turn changes the reservoir production predictions in this study we demonstrate the use of x ray computed tomography ct to investigate the porosity and permeability changes of cordova limestone samples during deformation in a triaxial cell the experiments were performed in a specially designed x ray transparent triaxial test cell which enables applying stress as well as making flow measurements because the presence and value of confining pressure changes the deformation behaviour of the rock different constant confining stresses were applied to the samples to change the deformation regime as the axial load was increased samples were scanned at different locations to determine the stress dependent local changes in porosity absolute permeability during the deformation was also measured results show that the stress condition applied to the porous medium changes the rock and fluid transport properties compared to measurements taken without stressing the sample x ray ct enabled the local porosity changes to be quantified to locate compaction bands and places where shear location occurs and to evaluate how the inner structure of the rock changes during different modes of deformation