eddy activity and mixing in upwelling systems a comparative study of northwest africa and california regions a comparative modeling approach is used to study the mesoscale dynamics of coastal transition zones in the upwelling systems of western sahara and central california it is shown that large differences in eddy activity and mixing exist between the two systems since upwelling favorable winds off central california and western sahara have similar amplitudes we suggest that observed and modeled differences in eddy activity are due to differences in configuration parameters it is argued that two of these parameters stratification and topography eventually affect the energy available for the mesoscales through baroclinic instability the large difference in stratification appears to be linked to the salinity structure formed by the large scale circulation and is directly related to available potential energy the shape of the continental shelf affects the position structure and scale of the ekman divergence hence upwelling intensity and frontal formation the potential impact of mesoscale eddy mixing and its variability on upwelling ecosystems is discussed

effects of wind stress and wind stress curl variability on coastal upwelling abstract aircraft measurements during the winter 1989 shelf mixed layer experiment smile and summer 1982 coastal ocean dynamics experiment code were used to characterize the spatial variation of the low level wind and wind stress over the northern california shelf the curl of the wind stress was calculated from directly measured turbulent stress components the accuracy of the computed curl was estimated to be adequate to map the spatial structure wintertime measurements showed a concentration of large positive curl over 1 pa 100 km 1 west of point arena regardless of wind direction due to the effects of the coastal topography on the wind fields results from summertime measurements showed a similar local maximum of positive curl west of point arena larger curl values over 3 5 pa 100 km 1 however were observed across a hydraulic jump propagating from stewarts point for highly supercritical marine boundary layer flow a two layer vertically integrated numerical model of coastal upwellin

fractal analysis applied to cataclastic rocks abstract cataclastic rocks can be characterized by their fractal dimension which is dependent on the mode of fragmentation a mode of fragmentation may be defined in terms of base b and the number of fragile elements n f fractal dimension of a cataclastic rock can be obtained by finding the slope of the least square fit straight line of particle size frequency area frequency and volume frequency distribution in a log log coordinate system the relationships are d slope size frequency d 2slope area frequency and d 3slope volume frequency respectively in the analyses particle shape does not affect fractal dimension and neither does the diameter measured for a cataclastic rock

subsurface fine scale patterns in an anticyclonic eddy off cap vert peninsula observed from glider measurements glider measurements acquired along four transects between cap vert peninsula and thecape verde archipelago in the eastern tropical north atlantic during march april 2014 were used to investigate fine scale stirring in an anticyclonic eddy the anticyclone was formed near 12 n off the continental shelf and propagated northwest toward the cape verde islands at depth between 100 and 400 m the isolated anticyclone core contained relatively oxygenated low salinity south atlantic centralwater while the surrounding water masses were saltier and poorly oxygenated the dynamical and thermohaline subsurface environment favored the generation offine scale horizontal and vertical temperature and salinity structures in and around the core of the anticyclone these features exhibited horizontal scales of o 10 30 km relatively small with respect to the eddy radius of o 150 km the vertical scales of o 5 100 m were associated to density compensated gradient spectra of salinity and oxygen along isopycnals revealed a slope of around k 2in the 10 to 100 km horizontal scale range further analyses suggest that the fine scale structures are likely related to tracer stirring processes such mesoscale anticyclonic eddies and the embedded fine scale tracers in and around them could play a major role in the transport of south atlantic central water masses and ventilation of the north atlantic oxygen minimum zone

mesoscale frontal structures in the canary upwelling system new front and filament detection algorithms applied to spatial and temporal patterns abstract an improved automatic detection of mesoscale frontal activity is proposed based on the edge detection algorithm initially presented by cayula and cornillon 1992 the performance and the sensitivity of their original method have been extensively tested on a very large modis sst data set at 1 km resolution over the canary upwelling system and compared to the results of a classic gradient based method its evaluation including the companion method using a contour following algorithm shows that a significant part of the fronts was not detected by the earlier method despite an overall robustness we propose here an improved implementation of the single image edge detection algorithm from the best combination of multiple detections based on sliding windows referred to as cmw the results show a very significant increase of the overall performance using a time series of 6 years 1 988 images we observed an average increase of 140 in the edge detection and 30 improvement in the average length of the segments additionally the sensitivity to the size of the detection window is lower and the necessity of using the following algorithm is greatly reduced we applied the cmw improvements to the canary current system and showed frontal activity developed along the whole coast with more intense fronts between cape ghir 30 30 n and cape beddouza 32 30 n and between cape juby 28 n and cape bojador 26 30 n the highest filament activity was associated with cape bojador followed by cape ghir and cape blanco 21 n considering the seasonality two main areas were identified north and south of cape juby with marked seasonality in the fronts and filaments no major interannual differences in frontal activity were observed in 2002 2007 except less seasonality during 2007

petroleum geology of tunisia recent discoveries and important oil shows have proven the existence of hydrocarbons in newly identified depocenters and reservoirs in general except for some areas around the producing fields tunisia is largely underdrilled the national company etap has decided to release data and to publish a synthesis on the petroleum geology of tunisia the geology of tunisia provides a fine example of the contrast between alpine folding which typifies northern tunisia and the african craton area of the saharan part eastern tunisia corresponds to an unstable platform forming plains or low hills and extending eastwards to the shallow pelagian sea there are a wide variety of basins central and northern tunisia represents a front basin the saharan ghadames basin or the chott trough are sag basins the gulf of gabes was formed as a distension margin the gulf of hammamet is a composite basin and several transversal grabens cut across the country including offshore and are rift type basins all these features are known to be oil prolific throughout the world two large fields and many modest size pools are known in tunisia oil and gas fields in the surrounding countries namely the saharan fields of algeria and libya the large bouri fieldmore offshore tripolitania and discoveries in the italian part of the straits of sicily suggest a corresponding potential in tunisia exposed paleogeographic and structural maps balanced sections and examples of fields and traps will support an optimistic evaluation of the future oil exploration in tunisia less

sst patterns and dynamics of the southern senegal gambia upwelling center the southern end of the canary current system comprises of an original upwelling center that has so far received little attention the southern senegal gambia upwelling center ssuc we investigate its dynamical functioning by taking advantage of favorable conditions in terms of limited cloud coverage analyses and careful examinations of over 1500 satellite images of sea surface temperature scenes contextualized with respect to wind conditions confirm the regularity and stability of the ssuc dynamical functioning as manifested by the recurrence and persistence of particular sst patterns the analyses also reveal subtle aspects of its upwelling structure shelf break cooling of surface waters consistent with internal tide breaking mixing complex interplay between local upwelling and the mauritanian current off the cape verde headland complexity of the inner shelf mid shelf frontal transition the amplitude of the diurnal cycle suggests that large uncertainties exist in the ssuc heat budget the studies limitations underscore the need for continuous in situ measurement in the ssuc particularly of winds

elastic stress control on the pattern of tensile fracturing around a small fault network at nash point uk abstract complex trajectories of fault related opening mode fractures at nash point in south wales uk are consistent with elastic stress fields computed for the observed fault network subject to north south compression the linear elasticity theory is used to calculate local stress increments produced by slip on the fault network faults are assumed to be free of shear stress and to slip in response to some remote stress load brittle failure of rock within this stress field is determined according to a combined griffith coulomb criterion discrete fracture networks are simulated according to simple growth rules where fractures initiate according to the state of brittle failure and propagate along a surface normal to the direction of most tensile local stress results demonstrate the dominant opening mode fracture were caused by a uniform body force e g unloading and are just locally perturbed by the pre existing fault network fault heights of 2 3 times the mean fault block width and regional contraction along an azimuth of 180 10 are required to reproduce the observed fracture pattern independent kinematic analysis of nearby faults yield estimates of the azimuth of regional contraction of 170 180 some features in the observed fracture pattern are not well reproduced but these are small scale and related to small scale irregularities on the fault planes

upwelling filaments off cap blanc interaction of the nw african upwelling current and the cape verde frontal zone eddy field 1 the hydrographical and dynamical properties of the upwelling filaments forming off cap blanc mauritania are investigated using remotely sensed and in situ data collected in april may 2009 during the strongest upwelling season the area is situated at the southern edge of the nw african upwelling system where the cape verde frontal zone cvfz separates warmer saltier north atlantic central water nacw and cooler fresher south atlantic central water sacw sea surface temperature images indicated the presence of an upwelling filament extending 280 km offshore rooted over the cap blanc promontory and entrained around a warm core anticyclonic eddy after this filament started to decay a new cold filament developed at the approximate same location high resolution moving vessel profiler mvp and acoustic doppler current profiler adcp surveys of these mesoscale structures revealed that both filaments were carrying south atlantic central water sacw offshore through an intense jet like flow similarity of the relative vorticity structure across the filament with that of the tangent eddy suggested that the latter was responsible for the offshore current tracking of this eddy in altimetric data demonstrated that it originated from the cvfz as implied by its hydrographic structure altimetric data also revealed that another anticyclonic structure centered over the cap blanc promontory was responsible for the northwestward advection of sacw into the base of the filament the results support the idea that some upwelling filaments can be produced by the interaction of an external eddy field including topographic eddies with the upwelled water

dynamics of a low enrichment high retention upwelling center over the southern senegal shelf senegal is the southern tip of the canary upwelling system its coastal ocean hosts an upwelling center which shapes sea surface temperatures between latitudes 12 and 15 n near this latter latitude the cape verde headland and a sudden change in shelf cross shore profile are major sources of heterogeneity in the southern senegal upwelling sector ssus ssus dynamics is investigated by means of regional ocean modeling system simulations configuration realism and resolution x 2 km are sufficient to reproduce the ssus frontal system our main focus is on the 3 d upwelling circulation which turns out to be profoundly different from 2 d theory cold water injection onto the shelf and upwelling are strongly concentrated within a few tens of kilometers south of cape verde and largely arise from flow divergence in the alongshore direction a significant fraction of the upwelled waters are retained nearshore over long distances while travelling southward under the influence of northerly winds another source of complexity regional scale alongshore pressure gradients also contributes to the overall retention of upwelled waters over the shelf varying the degree of realism of atmospheric and oceanic forcings does not appreciably change these conclusions this study sheds light on the dynamics and circulation underlying the recurrent sea surface temperature pattern observed during the upwelling season and offers new perspectives on the connections between the ssus physical environment and its ecosystems it also casts doubt on the validity of upwelling intensity estimations based on simple ekman upwelling indices at such local scales

the seismicity geomorphology and structural evolution of the corinth area of greece in the eastern gulf of corinth geological structure is closely reflected in the topography in the 1981 corinth earthquakes ground deformation accentuated existing geomorphological patterns we explore the relationship between seismicity and landforms in space and time the area examined extends beyond the epicentral region of the 1981 events and its evolution is traced over the last 40000 years to understand the relation between deep and superficial structures we discuss processes that occurred in the 1981 earthquakes and go on to propose that surface faulting appears only above linear faults at depth that move in earthquakes with magnitudes m s greater than six where faults at depth intersect or bend the faulting becomes distributed and prim ary faulting does not reach the surface here the surface manifestation of faulting at depth is surface folding and secondary faulting such regions are identified in maps of the eastern gulf of corinth evidence for the evolution of the fault systems is provided by eyewitness accounts of shoreline changes following the recent earthquakes historical and archaeological data pertaining to old sea levels and 14 c dates for molluscs collected from fossil shorelines the results of these studies broadly confirm an earlier view of j a jackson et al earth planet sci lett 57 377 397 1982 that motion has shifted from faulting south of the city of corinth to faulting in the perachora peninsula but the transfer is not complete areas lying between the two fault systems have moved up and down in historical and archaeological times indicating that both systems are still active the evidence for activity of the northern system points to a repeat time of 300 years for earthquakes com parable with those of 1981 the work discussed in this paper suggests that some of the features previously described as m arine terraces are fault controlled continental surfaces furtherm ore beach deposits at a num ber of different levels long regarded as successive shorelines are in fact contemporaneous the critical ages were obtained by radiocarbon dating of shell carbonate a technique which yields dependable results if applied to samples which have been carefully selected and pretreated palaeontological dating of the terraces in contrast is found to be misleading because the faunas are environm entally controlled and consequently diachronous

sea surface temperature fronts in the california current system from geostationary satellite observations 1 sea surface temperature sst fronts are determined for the 2001 2004 time period from geostationary operational environmental satellites goes data in the california current system ccs the probability of detecting a sst front at an individual pixel location in the ccs is presented as a bi monthly climatology fronts clearly indicate the seasonal evolution of coastal upwelling as well as meanders and filaments that are often linked with irregularities in coastline geometry winter is characterized by low frontal activity along the entire coast fronts first appear close to the coast during spring particularly south of cape blanco where upwelling favorable winds are already persistent the area of high frontal activity continues to increase during summer especially between monterey bay and cape blanco extending more than 300 km from the coast the region with high frontal activity widens at 2 6 km day 1 off northern baja california a band with persistent fronts is found close to the coast year round but there is no evidence of a seasonal widening of the area of higher activity during fall the weakening of upwelling favorable winds leads to a gradual decrease in frontal activity an empirical orthogonal function eof decomposition reveals the development of sst fronts associated with seasonal upwelling for locations north of monterey bay with less summer intensification to the south the first appearance of fronts close to the coast during spring and the occurrence of the fronts offshore later in the season are represented by additional statistically significant eof modes

elastic dislocation modelling for prediction of small scale fault and fracture network characteristics predictingthe effects of small scale faults and fractures on reservoirbehaviour requires a definition of their spatial distribution orientation and mode elastic dislocation ed theory can predict the distribution of displacement strain and stress in the rock volume surrounding major faults from mapping of fault geometry and slip distribution in 3d seismic reflection datasets the intensity of small scale faulting can be related to the predicted local strain or the degree to which the shear stresses exceeded the rock failure envelope we illustrate the methodology with three case studies i a relatively simple thrust anticline from venezuela where hydro carbons are trapped in pliocene sandstones within the faulted hanging wall anticline ii the gull faks field and of the north sea and iii the miskar field offshore tunisia where large seismically mapped normal faults are forward modelled to predict small scale fault characteristics for comparison with detailed interpretation and seismic attribute analysis key requirements for the development of a robust predictive model of the small scale fault and fracture network are a geometrically consistent framework model judicious choice of mechanical properties and a reasonable estimate of regional background strain

fracture prediction for the 1980 el asnam algeria earthquake via elastic dislocation modeling 1 geomechanical models based on linear elasticity have been used to predict the mode and distribution of subseismic fractures around larger faults these models can be tested against field observations of surface breaks fractures formed in the aftermath of large earthquakes this paper presents forward models based on elastic dislocation theory of the deformation due to the ms 7 3 earthquake at el asnam algeria in 1980 using fault parameters from previous geodetic studies to define a set of larger faults our models calculate the deformation field in the surrounding rock volume we compare predicted strain and stress fields with the surface deformation measured in the area following the 1980 earthquake using a combination of the redistributed elastic dislocation stress due to slip on the major faults and a small component of overburden stress the models successfully predict normal faults and tensile fractures in the hanging wall of the reverse fault system orientations of the predicted faults vary along strike of the fault system being parallel to the main reverse fault in the south but oblique to it along the central segment agreeing with observed surface breaks the results of our forward modeling are not sensitive to the magnitude or direction of a regional tectonic stress the predicted fractures are controlled by the near field short term redistributed stresses due to coseismic slip the agreement between modeled and measured deformation patterns adds confidence in the use of elastic dislocation theory to accurately predict small faults generated by coseismic slip on large faults

a small scale oceanic eddy off the coast of west africa studied by multi sensor satellite and surface drifter data a small scale oceanic eddy which was generated in autumn 2011 at the headland of cap vert off the coast of senegal west africa and then propagated westward into the open north atlantic ocean is studied by multi sensor satellite and surface drifter data the eddy was generated after a sudden increase of the trade winds causing an enhanced southward flow and upwelling at the coast of senegal after this wind burst event an extremely nonlinear cyclonic eddy with a radius of about 10 to 20 km evolved downstream of cap vert with rossby number larger than one our analysis suggests that the eddy was generated by flow separation at the headland of cap vert the eddy was tracked on its way into the open north atlantic ocean from satellites over 31 days via its sea surface temperature and chlorophyll a chl signature and by a satellite tracked surface drifter the satellite images show that this small scale eddy transported nutrients from the upwelling region westward into the oligotrophic north atlantic thus giving rise to enhanced chl concentration there maximum chl concentration was encountered few days after vortex generation which is consistent with a delayed plankton growth following nutrient supply into the euphotic zone within the eddy furthermore the eddy was imaged by the synthetic aperture radar sar onboard the envisat satellite it is shown that the radar signatures of cold eddies result from damping of short surface waves by biogenic surface films which arise from surface active material secreted by the biota in the cold eddy as well as by the change of the stability of the air sea interface highlights processes during the onset of coastal upwelling off west africa multi sensor remote sensing and in situ observations highly nonlinear small scale eddy generation at cap vert nrcs reduction in parts of the eddy due to biogenic surface films

the marine layer off northern california an example of supercritical channel flow abstract during the spring and summer northerly winds driven by the north pacific high pressure system are prevalent over the northern california continental shelf only interrupted for periods of a few days when weak or southerly winds occur in the course of the coastal ocean dynamics experiment code fixed station and observations were made to describe the temporal and spatial structure of the lower atmosphere and their relation to the strong upwelling of coastal waters in a region extending up to 40 km offshore and 100 km along the coast these observations suggest that atmospheric conditions during the spring and summer usually fall into one of three categories the surface wind can be everywhere weak pattern 1 it can blow at large speeds in a uniform pattern pattern 2 or finally the structure of the northerly surface wind can be complex with large changes in the wind speed and corresponding changes in the surface pressure over short spatial scales pattern 3 the latter pattern which o

coastal perturbations of marine layer winds wind stress and wind stress curl along california and baja california in june 1999 abstract month long simulations using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 with a horizontal resolution of 9 km have been used to investigate perturbations of topographically forced wind stress and wind stress curl during upwelling favorable winds along the california and baja california coasts during june 1999 the dominant spatial inhomogeneity of the wind stress and wind stress curl is near the coast wind and wind stress maxima are found in the lees of major capes near the coastline positive wind stress curl occurs in a narrow band near the coast while the region farther offshore is characterized by a broad band of weak negative curl curvature of the coastline such as along the southern california bight forces the northerly flow toward the east and generates positive wind stress curl even if the magnitude of the stress is constant the largest wind stress curl is simulated in the lees of point conception and the santa ba

diurnal warm layer events in the western mediterranean and european shelf seas we characterize near surface ocean diurnal warm layer events using satellite observations and fields from numerical weather forecasting the study covers april to september 2006 over the area 11 degrees w to 17 degrees e and 35 degrees n to 57 degrees n with 0 1 degrees cells we use hourly satellite ssts from which peak amplitudes of diurnal cycles in sst dssts can be estimated with error similar to 0 3 k the diurnal excursions of sst observed are spatially and temporally coherent the largest dssts exceed 6 k affect 0 01 of the surface and are seen in the mediterranean north and irish seas there is an anti correlation between the magnitude and the horizontal length scale of dsst events events wherein dsst exceeds 4 k have length scales of 40 km from the frequency distribution of different measures of wind speed minima we infer that extreme dsst maxima arise where conditions of low wind speed are sustained from early morning to mid afternoon

transport and retention in an upwelling region the role of across shelf structure abstract the paradox of upwelling is the relationship between strong wind forcing nutrient enrichment and shelf productivity here we investigate how across shelf structure in velocity and hydrography plays a role in the retention inshore and export offshore of particles such as nutrients plankton and larvae we examine the spatial structure of the coastal currents during wind driven upwelling and relaxation on the northern californian shelf the field work was conducted as part of the wind events and shelf transport west project a 5 year nsf coop funded study of the role of wind driven transport in shelf productivity off bodega bay northern california from 2000 to 2003 we combine shipboard velocity profiles adcp and water properties from hydrographic surveys during the upwelling season to examine the mean across shelf structure of the hydrography and velocity fields during three contrasting upwelling seasons and throughout the upwelling relaxation cycle we also present results from two winter seasons that serve as contrast to the upwelling seasons during all three upwelling seasons clear spatial structure is evident in velocity and hydrography across the shelf exemplified by current reversals inshore and the presence of a persistent upwelling jet at the shelf break this jet feature changes in structure and distance from the coast under different wind forcing regimes the jet also changes from the north of our region where it is a single narrow jet adjacent to the coast and to the south of our region where it broadens and at times two jets become evident we present observations of the california under current which was observed at the outer edge of our domain during all three upwelling seasons the observed across shelf structure could aid both in the retention of plankton inshore during periods of upwelling followed by relaxation and in the export of plankton offshore in the upwelling jet

ecological zonation of zooplankton in the coast study region off central oregon in june and august 2001 with consideration of retention mechanisms 1 to determine the mechanisms that might explain retention and or loss of plankton during the coastal upwelling season one needs an understanding of the vertical migration behavior and ontogenetic changes in vertical distribution and data on direction and magnitude of currents at depths where the animals reside in this paper we compare and contrast the cross shelf distributions of four copepod species calanus marshallae pseudocalanus mimus acartia longiremis and centropages abdomalis and the euphausiid euphausia pacifica from sampling during the coastal ocean advances in shelf transport coast program the coast study region was off central oregon 44 45 n ranged from the nearshore zone out to 1000 m isobath and was a trapezoid 120 km in length and 40 km wide in the north by 100 km wide in the south plankton were sampled along three transects in the north middle and southern portions of the study region for the two most abundant copepods c marshallae and p mimus sampling with a multiple opening closing net and environmental sampling system showed that naupliar and early copepodite stages were found within the warm phytoplankton rich upper 20 m of the water column but that copepodite stages c3 through adult were found at progressively deeper strata in the water column similarly euphausiid larvae were most abundant within the upper 20 m whereas juveniles and adults lived deeper in the water column diel vertical migration was observed only in the older developmental stages because older stages occupy different strata than younger stages there is cross shelf displacement of zooplankton

on the dynamics of the southern senegal upwelling center observed variability from synoptic to superinertial scales upwelling off southern senegal and gambia takes place over a wide shelf with a large area where depths are shallower than 20 m this results in typical upwelling patterns that are distinct e g more persistent in time and aligned alongshore from those of other better known systems including oregon and peru where inner shelves are comparatively narrow synoptic to superinertial variability of this upwelling center is captured through a 4 week intensive field campaign representing the most comprehensive measurements of this region to date the influence of mesoscale activity extends across the shelf break and far over the shelf where it impacts the midshelf upwelling e g strength of the upwelling front and circulation possibly in concert with wind fluctuations internal tides and solitary waves of large amplitude are ubiquitous over the shelf the observations suggest that these and possibly other sources of mixing play a major role in the overall system dynamics through their impact upon the general shelf thermohaline structure in particular in the vicinity of the upwelling zone systematic alongshore variability in thermohaline properties highlights important limitations of the 2d idealization framework that is frequently used in coastal upwelling studies