variability in the canary islands area of filament eddy exchanges abstract the physical background to a suite of biological studies carried out in the canary islands upwelling region is presented the area is unique in that the coastal transition zone is spanned by an archipelago of islands that shed mesoscale eddies of diameter 50 100 km into the alongshore flow a recurrent filament and eddy system was sampled intensively to study the changing properties of waters as they are advected towards the open ocean in the filament and to investigate the exchanges between filament and eddies the system was more complex than previously revealed in early august a single filament extended offshore from near cape juby two weeks later a second filament had developed slightly farther north and extended offshore to merge with the first at 100 km offshore the merged filament was entrained around a recurrent topographically trapped cyclonic eddy and interacted with transient cyclonic and anticyclonic eddies shed from the island of gran canaria between the two filaments and the coast a pair of counter rotating eddies re circulated water parcels for several weeks surface layer drifters cycled around this near shore re circulation several times before following convoluted paths that demonstrate significant exchange between continental shelf and open ocean waters

nutrient irrigation of the north atlantic abstract the north atlantic as all major oceans has a remarkable duality in primary production manifested by the existence of well defined high and low mean primary production regions the largest region is the north atlantic subtropical gyre nastg an anticyclone characterized by bowl shaped isopycnals and low production the nastg is surrounded at its margins by smaller cyclonic high production regions where these isopycnals approach the sea surface the most extensive cyclonic regions are those at the latitudinal extremes i e the subpolar and tropical oceans though smaller ones do occur at the zonal boundaries in this article we review historical data and present new analyses of climatological data and a selected number of hydrographic cruises in the western northwestern and eastern southeastern boundaries of the nastg with the objective of investigating the importance of upward epipycnal advection of nutrient rich subsurface layers irrigation in maintaining high primary production in the euphotic layers in the north atlantic subpolar gyre naspg irrigation implies intergyre exchange caused by the outcropping extension of the gulf stream gs following the formation of the deep winter mixed layer in the eastern boundary of the nastg irrigation is attained through a permanent upwelling cell which feeds the canary upwelling current cuc in the southeastern corner irrigation occurs in fall when the guinea dome gd is reinforced and in winter when the cuc reaches its southernmost extension other characteristics of the north south extension of the gs cuc are the seasonal nutrient replenishing of subsurface layers spring restratification of naspg and winter relaxation of the gd and the maintenance of high levels of diapycnal mixing during the last phase of nutrient transfer to the euphotic layers off the mid atlantic bight the gs transports a total of about 700 kmol s 1 of nitrate with almost 100 kmol s 1 carried in the surface

the faroe shetland basin a regional perspective from the paleocene to the present day and its relationship to the opening of the north atlantic ocean the faroe shetland basin is located offshore nw scotland on the se margin of the atlantic ocean and comprises numerous sub basins and intra basin highs that are host to a number of significant hydrocarbon discoveries the principal hydrocarbon discoveries are in palaeocene eocene strata though earlier ones are known and therefore their existence is intimately linked to the opening and evolution of the north atlantic from 54 ma the final rifting and separation of greenland from eurasia is commonly attributed to the arrival of a mantle plume which impacted beneath greenland in the early tertiary moreover the ensuing plate separation is commonly described in terms of instantaneous unzipping of the north atlantic whereas in reality proto plate boundaries were more diffuse during their inception and the linked rift system including connections with the arctic which we see today was not established until late palaeogene early neogene time from a regional analysis of ocean basin development including the stratigraphic record on the adjacent continental margins the significance of the greenland iceland faroe ridge and the age and role of iceland we propose a dual rift model whereby north atlantic breakup was only partial until the oligo miocene with true final breakup only being achieved when the reykjanes and kolbeinsey ridges became linked as final breakup coincides with the appearance of iceland this model negates the need for a plume to develop the north atlantic with rifting reliant on purely plate tectonic mechanisms lithospheric thinning and variable decompressive upper mantle melt along the rifts

in situ production of 36cl in uranium ore a hydrogeological assessment tool in situ neutron activation of 35cl within the rock and groundwater of geologic deposits that have elevated concentrations of uranium provides a hydrogeological tracer we determine the production rate and mobility of 36cl in the 1 3 billion year old cigar lake uranium ore deposit accelerator mass spectrometry was used to map the concentrations of 36cl in the ore and in the groundwater that were up to 100 times greater than those encountered in unmineralized portions of the host sandstone aquifer the residence time of this mobile anion in groundwater within the mineralized zone ranged from 14 to 280 kyr these residence times are consistent with the hydraulic and geochemical data suggesting significant control of cl and groundwater movement by the clay rich matrix of the mineralized zone

dynamics of the india eurasia collision zone we present simple new dynamic calculations of a vertically averaged deviatoric stress field over a depth average of 100 km for asia from geodetic geologic topographic and seismic data a first estimate of the minimum absolute magnitudes and directions of vertically averaged deviatoric stress is obtained by solving force balance equations for deviatoric stresses associated with gravitational potential energy differences within the lithosphere plus a first order contribution of deviatoric stresses associated with stress boundary conditions this initial estimate of the vertically averaged deviatoric stress field is obtained independent of assumptions about the rheology of the lithosphere absolute magnitudes of vertically averaged deviatoric stresses vary between 5 and 40 mpa assuming bulk viscous behavior for the lithosphere the magnitudes of deviatoric stresses together with the magnitudes of strain rates inferred from quaternary fault slip rate and gps data yield vertically averaged effective viscosities for tibet of 0 5 5 1022 pa s compared with 1 2 5 1023 pa s in more rigid areas elsewhere in the region a forward modeling method that solves force balance equations using velocity boundary conditions allows us to refine our estimates of the vertically averaged effective viscosity distribution and deviatoric stress field the total vertically averaged deviatoric stress and effective viscosity field are consistent with a weak lower crust in tibet they are consistent with some eastward motion of tibet and south china lithosphere relative to eurasia and they confirm that gravitational potential energy differences have a profound effect on the spatially varying style and magnitude of strain rate around the tibetan plateau our results for the vertically averaged deviatoric stress argue for a large portion of the strength of the lithosphere to reside within the seismogenic upper crust to get deviatoric stress magnitudes there to be as high as 100 300 mpa in accord with laboratory and theoretical friction experiments indicating that stress drops in earthquakes are small fractions of the total deviatoric stress

surface motions and intraplate continental deformation in alaska driven by mantle flow the degree to which the lithosphere and mantle are coupled and contribute to surface deformation beneath continental regions remains a fundamental question in the field of geodynamics here we use a new approach with a surface deformation field constrained by gps geologic and seismicity data together with a lithospheric geodynamic model to solve for tractions inferred to be generated by mantle convection that 1 drive extension within interior alaska generating southward directed surface motions toward the southern convergent plate boundary 2 result in accommodation of the relative motions between the pacific and north america in a comparatively small zone near the plate boundary and 3 generate the observed convergence within the north american plate interior in the mackenzie mountains in northwestern canada the evidence for deeper mantle influence on surface deformation beneath a continental region suggests that this mechanism may be an important contributing driver to continental plate assemblage and breakup

alteration of uraninite from the nopal i deposit pen a blanca district chihuahua mexico compared to degradation of spent nuclear fuel in the proposed u s high level nuclear waste repository at yucca mountain nevada abstract at the nopal i uranium deposit primary uraninite nominally uo 2 x has altered almost completely to a suite of secondary uranyl minerals the deposit is located in a basin and range horst composed of welded silicic tuff uranium mineralization presently occurs in a chemically oxidizing and hydrologically unsaturated zone of the structural block these characteristics are similar to those of the proposed u s high level nuclear waste hlw repository at yucca mountain nevada petrographic analyses indicate that residual nopal i uraninite is fine grained 5 10 m and has a low trace element content average about 3 wt these characteristics compare well with spent nuclear fuel the oxidation and formation of secondary minerals from the uraninite have occurred in an environment dominated by components common in host rocks of the nopal i system e g si ca k na and h 2 o and also common to yucca mountain in contrast secondary phases in most other uranium deposits form from elements largely absent from spent fuel and from the yucca mountain environment e g pb p and v the oxidation of nopal i uraninite and the sequence of alteration products their intergrowths and morphologies are remarkably similar to those observed in reported corrosion experiments using spent fuel and unirradiated uo 2 under conditions intended to approximate those anticipated for the proposed yucca mountain repository the end products of these reported laboratory experiments and the natural alteration of nopal i uraninite are dominated by uranophane nominally ca uo 2 2 si 2 o 7 6h 2 o with lesser amounts of soddyite nominally uo 2 2 sio 4 2h 2 o and other uranyl minerals these similarities in reaction product occurrence developed despite the differences in time and physical chemical environment between yucca mountain approximate laboratory experiments and yucca mountain approximate uraninite alteration at nopal i suggesting that the results may reasonably represent phases likely to form during long term alteration of spent fuel in a yucca mountain repository from this analogy it may be concluded that the likely compositional ranges of dominant spent fuel alteration phases in the yucca mountain environment may be relatively limited and may be insensitive to small variations in system conditions

gplates building a virtual earth through deep time gplates is an open source cross platform plate tectonic geographic information system enabling the interactive manipulation of plate tectonic reconstructions and the visualization of geodata through geological time gplates allows the building of topological plate models representing the mosaic of evolving plate boundary networks through time useful for computing plate velocity fields as surface boundary conditions for mantle convection models and for investigating physical and chemical exchanges of material between the surface and the deep earth along tectonic plate boundaries the ability of gplates to visualize subsurface 3 d scalar fields together with traditional geological surface data enables researchers to analyze their relationships through geological time in a common plate tectonic reference frame to achieve this a hierarchical cube map framework is used for rendering reconstructed surface raster data to support the rendering of subsurface 3 d scalar fields using graphics hardware accelerated ray tracing techniques gplates enables the construction of plate deformation zones regions combining extension compression and shearing that accommodate the relative motion between rigid blocks users can explore how strain rates stretching shortening factors and crustal thickness evolve through space and time and interactively update the kinematics associated with deformation where data sets described by geometries points lines or polygons fall within deformation regions the deformation can be applied to these geometries together these tools allow users to build virtual earth models that quantitatively describe continental assembly fragmentation and dispersal and are interoperable with many other mapping and modeling tools enabling applications in tectonics geodynamics basin evolution orogenesis deep earth resource exploration paleobiology paleoceanography and paleoclimate

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

physical oceanography of the western iberia ecosystem latest views and challenges the present review is focused on the mesoscale physical processes recognized in the western iberia ecosystem complementing earlier reviews dedicated to larger scales recent studies support the idea that the mesoscale processes superimposed on the larger scale variability are the major factor controlling the ecosystem functioning in the region a complex structure of interleaved alongshore slope shelf and coastal currents that interact with eddies buoyant plumes upwelling filaments and fronts surface layer expressions of the subsurface circulation and internal waves is revealed by the latest research all of these contribute in different ways to have an effect on the ecosystem the supposedly less variable winter circulation also exhibits significant mesoscale activity in the form of eddy shedding from the poleward slope current intermittent upwelling events and transient nearshore poleward flows the present incomplete knowledge of this complex system presents a number of challenges and questions that must be addressed if we are to arrive at a satisfactory understanding and predictive capability for the system as a whole 2007 elsevier ltd all rights reserved

predicting plate velocities with mantle circulation models 1 we predict plate motions from a comprehensive inversion of theoretical estimates of tectonic forces in order to evaluate the relative importance of these and the uncertainties of such models plate driving forces from the mantle are calculated using global flow models that are driven by tomography and subduction derived density fields observed and predicted plate velocities agree well for a variety of models leading to varied conclusions about the relative importance of forces the dominance of the subduction related density pattern in the mantle is confirmed it appears that p wave models do not satisfactorily image all of the slab associated anomalies in the upper mantle furthermore lower mantle structure always improves the plate motion fit with respect to models that are based on upper mantle anomalies and lithospheric thickening only we show that the average torques from the lower mantle scale with the radial flow through the 660 km phase transition the amplitude of the lower mantle torques will be significant for a range of models if there is mass flux through 660 km we also evaluate parameterized edge forces and find that the additional inclusion of such torques does not significantly improve the model fit the main reason for the nonuniqueness of the inversions is plate boundary geometry since all plate motions are dominated by the trench ridge system and plates move from ridges to trenches

cenozoic tectonic and thermal history of the nenana basin central interior alaska new constraints from seismic reflection data fracture history and apatite fission track analyses the nenana basin of interior alaska forms a segment of the diffuse plate boundary between the bering and north american plates and is located within a complex zone of crustal scale strike slip deformation that accommodates compressional stresses in response to oblique plate convergence to the south the basin is currently the focus of new oil and gas exploration integration of seismic reflection and well data fracture data and apatite fission track analyses with regional data improves our understanding of the tectonic development of this continental strike slip basin the nenana basin formed during the late paleocene as a 13 km wide half graben affected by regional intraplate magmatism and localized crustal thinning across the minto fault in south central alaska the basin was uplifted and exhumed along this faulted margin in the early eocene through to late oligocene in response to oblique subduction along the southern alaska margin this event resulted in the removal of up to 1 5 km of late paleocen

paleoceanography of the mauritanian margin during the last two climatic cycles from planktonic foraminifera to african climate dynamics abstract the last 220 ka of the md03 2705 18 05 81 n 21 09 19 w sedimentary sequence retrieved off the cape verde islands was investigated using a multiproxy approach planktonic foraminifera assemblage analyses coupled with isotopic measurements 18 o from benthic planulina wuellerstorfi and planktonic globigerinoides ruber foraminifera monospecific samples were conducted along the topmost 11 m of the sequence high resolution x ray fluorescence measurements 0 5 cm resolution giving access to major element ratio have completed the geochemical analyses along the core seasonal and annual past sea surface temperatures sst were quantitatively reconstructed local sea surface salinity sss changes were then estimated by coupling sst with planktonic 18 o data our data provide a set of both oceanic and continental markers of environmental changes along the north western african margin the major changes detected in our record are discussed in the light of the regional paleoceanographic and paleoclimatic history of the last 220 ka coupled oceanographic and atmospheric processes portray the climatic evolution of the area and show strong links among the regional oceanography water mass advection the upwelling dynamics and the intertropical convergence zone itcz migration an increased upwelling activity or influence of upwelling filaments is noted at the end of the two last glacial periods probably in response to a more southerly position of the itcz higher sss are recorded over the area during arid intervals and were tentatively interpreted as signing a southward shift of the cape verde frontal zone a detailed coupling between dust advection and sss values over the site of study was noted during mis6 5

mesozooplankton in the canary current system the coastal ocean transition zone abstract the canary current system ccs is one of the largest upwelling areas of the world understanding the biogeochemical fluxes and recruitment of fish in relation to changes in climate requires knowledge of the factors influencing mesozooplankton biomass and fluxes here the trophic and metabolic characteristics of mesozooplankton for the oceanic upwelling and eddy system of the ccs are reviewed mesoscale phenomena are of importance in this region as besides upwelling filaments the eddy system shed from the canary islands is unique in comparison with other similar systems such as the humboldt california and benguela the coupling of production in the coastal area off northwest africa with the oceanic zone through filaments and eddies topographically formed in the coast or shed by the islands promotes a continuous transport of organic matter towards the deep ocean zooplankton follow the signal of the mesoscale phenomena and are good tracers of advection the different species which can be used as targets in the area are also described from the upwelling region to the open ocean however not all the variability in the area is explained by bottom up controls the effect of diel vertical migrants feeding on epipelagic zooplankton shows that top down controls are also important to understanding the structure and fluxes in this oceanic environment

three dimensional circulation in the nw africa coastal transition zone abstract high resolution data collected southeast of the canary islands during late winter 2006 are analyzed to describe the hydrography and three dimensional circulation in the coastal transition zone off nw africa the data are optimally interpolated over a regular grid the geostrophic velocity field is calculated and the q vector formulation of the omega equation is used to compute the quasi geostrophic qg mesoscale vertical velocity the coastal transition zone is divided into upwelling frontal and offshore regions with distinct physical and dynamic characteristics the upwelling region is characterized by cold and weakly stratified waters flowing towards the equator with a poleward undercurrent of approximately 0 05 m s 1 over the continental slope the frontal region exhibits a southwestward baroclinic jet associated with cross shore raising isopycnals the jet transport is close to 1 sv with maximum velocities of 0 18 m s 1 at surface decreasing to 0 05 m s 1 at 300 db vertical sections across the frontal region show the presence of deep eddies probably generated by the topographic blocking of the islands to the southward current as well as much shallower eddies that likely have arisen as instabilities of the baroclinic upwelling jet the qg mesoscale vertical velocity field is patchy estimated to range from 18 to 12 m day 1 with the largest absolute values corresponding to an anticyclonic eddy located south of fuerteventura island these values are significantly larger than estimates for other vertical velocities diapycnal vertical velocities associated with mixing in the frontal region a few meters per day and wind induced vertical velocities non linear ekman pumping arising from the interaction between the wind stress and the background vorticity maximum values of a few meters per day linear ekman pumping due to the divergence of ekman transport a fraction of a meter per day or the coastal constraint in the upwelling region about 0 7 m day 1 however the patchiness in both the qg mesoscale vertical velocity and the non linear ekman pumping velocity cause their integrated vertical transports to be one order of magnitude smaller than either coastal ekman transport 0 08 sv integrated linear ekman pumping 0 05 sv or diapycnal transfer about 0 1 0 2 sv the pattern of the near surface fluorescence field is a good indicator of these different contributions with large homogeneous values in the coastal upwelling region and a patchy structure associated with the offshore mesoscale structures

tectonic block motion and glacial isostatic adjustment in southeast alaska and adjacent canada constrained by gps measurements 1 we use data from campaign and continuous gps sites in southeast alaska and the neighboring region of canada to constrain a regional tectonic block model that estimates block angular velocities and derives a self consistent set of fault slip rates from the block motions present day tectonics in southeast alaska is strongly influenced by the collision of the yakutat block our model predicts a velocity of 50 3 0 8 mm a toward n22 9 0 6 w for that block our results suggest that the eastern edge of the yakutat block is deforming along this edge the fairweather fault accommodates a large portion of the pacific north america relative plate motion through 42 9 0 9 mm a of dextral slip further south along the queen charlotte fault our model predicts an average of 43 9 0 6 mm a of dextral slip and a southward increasing amount of transpression strain from the yakutat collision is transferred far to the east of the strike slip system this strain transfer causes the region north of glacier bay to undergo a clockwise rotation south of glacier bay and inboard of the queen charlotte fault a smaller but clearly defined clockwise rotation is observed the heterogeneous block motion north and south of glacier bay may indicate the area is undergoing internal deformation and could explain regional patterns of diffuse seismicity the northern cordillera of canada displays a small northeasterly motion our block model suggests that the entire southeastern alaska northwestern canada margin is mobile

u pb geochronology of minerals from the midwest uranium deposit northern saskatchewan analyses of u pb ratios in 30 microsamples of pitchblende and coffinite from the midwest uranium deposit in northern saskatchewan as well as two altered zircons from host rocks indicate an age of

on the strength of interplate coupling and the rate of back arc convergence in the central andes an analysis of the interseismic velocity field 1 we interpret the interseismic crustal velocity field of the central andes using a simple three plate model in which the andean mountain belt is treated as a rigid microplate located between the nazca and south american soam plates we assume that the euler vectors associated with these plates are strictly coaxial and that the surface velocity field can be decomposed into an elastic loading field driven by locking of the main plate boundary and a smaller contribution associated with back arc convergence we obtain our best fit to the geodetic velocities if the main plate boundary is fully 100 locked between depths of 10 50 km and 8 5 of nazca soam plate convergence is achieved in the back arc by underthrusting of the brazilian shield beneath the subandean zone

alkaline phosphatase activity and its relationship to inorganic phosphorus in the transition zone of the north western african upwelling system abstract the enzymatic activity of alkaline phosphatase apa was studied in the transition zone between the african upwelling system and the open ocean waters of the canary islands region this region is recurrently dominated by the presence of upwelling filaments that may transport nutrient enriched waters out into the open ocean before nutrients become exhausted by plankton turnover rates by apa were generally low in the whole region but detectable in all the measurements carried out on average turnover rates were higher in the upwelling stations and apa in those waters seemed to be mainly generated by heterotrophic bacteria to supply easily assimilable organic c apa outside the upwelling area showed an inverse hyperbolic relationship with increasing phosphate suggesting the presence of both constitutive and pi inducible apa in these offshore waters a threshold of 0 1 m of phosphate could be defined for the regulatory function of pi on apa thus apa in nutrient poor waters seemed to be induced to compensate for pi deficiency turnover rates in the filaments showed basal probably constitutive levels whereas they increased in the surrounding waters where phosphate concentration presumably did not satisfy plankton p demands the fertilising effect of the filaments and associated cyclonic eddies extended to at least 175 km offshore where basal alkaline phosphatase activities were still found the magnitude of this effect depends probably on the intensity of upwelling events and the degree of recirculation of filament water back to the coastal jet

canary current and north equatorial current from an inverse box model 1 the large scale canary basin circulation is estimated from a box inverse model applied to hydrographic data from a quasi synoptic survey carried out in september 2003 the cruise consisted of 76 full depth ctd and oxygen stations circulation is required to nearly conserve mass and anomalies of salinity and heat within layers bounded by neutral surfaces it permits advective and diffusive exchange between layers and an adjustment of the ekman transport and the freshwater flux divergences the canary current at the thermocline layer transports a net mass of 4 7 0 8 sv southward north of the canary islands from the african coast to 19 w it is divided into a northward circulation at a rate of 1 1 0 5 sv between the african coast and lanzarote island and a southward transport of 5 8 0 6 sv it transports north atlantic central water and organic matters advected offshore by the filaments protruding from the upwelling system off northwest africa at 24 n the canary current feeds the north equatorial current that transports a mixture of north and south atlantic central waters westward in the intermediate layer a southwestward flow of 1 2 1 1 sv transports mediterranean water to the subtropical gyre though the highest salt flux is transported by a meddy oxygen distribution and mass transport suggest a northeastward deep flow of a water mass colder than 2 2 c consisting of diluted antarctic bottom water the heat and freshwater divergences and the average dianeutral velocity and diffusion between the sections and the african coast are negligible

thorium and uranium contents of gneisses and trondhjemites in the western dharwar craton india widespread metasomatic addition of u has apparently occurred in archean tonalitic trondhjemitic gray gneisses in the western dharwar craton of southern india gneisses of 3200 3000 ma age near the holenarasipur schist belt contain average concentrations of about 10 ppm th and 3 5 ppm u the u is considerably more abundant than average u 1 5 ppm in archean gray gneisses of the superior province of the canadian shield and consequently the th u ratios are low in the indian gneisses comparatively massive trondhjemitic plutons associated with a 3000 ma event in the dharwar craton are very depleted in both th and u and we propose that the metasomatism of the gneisses occurred while the plutons were being emplaced and were expelling fluids from the magmas there is no evidence for metasomatism 2500 ma ago the age of extensive granulite metamorphism in southern india

the role of isotope geochemistry studies in the canadian nuclear fuel waste management program abstract the objective of the canadian nuclear fuel waste management program is to develop and assess a method for the safe disposal of used nuclear fuel wastes from canadian nuclear power generating facilities the concept that is being developed involves the disposal of these wastes in a cavity mined at a depth of 500 1000 m in a plutonic rock formation both in the assessment of this concept and in any possible future site selection the geochemistry of the rock formation and of the groundwater plays a significant role isotope geochemistry studies involve the determination of the distribution and behaviour of stable and radioactive isotopes in the groundwater and in the rock matrix this information can be used to shed light on the geochemical history of the rock formation under investigation and increase the understanding of the geochemical processes that govern the evolution of these rock formations the information can in principle also be used to date the various geological events and processes that have led to the distribution of radioactive isotopes in the rock and in the groundwater

the eastern boundary current system between the canary islands and the african coast to study the easternboundarycurrentsystem off northwest africa in detail several ctd adcp sections and long term mooring work were carried out in the channel between lanzarote and africa the observations are compared with a fine resolution model which was developed in the framework of the canigo project the water masses which are observed in this area are characterised and classified in density ranges the current field shows a high spatial and temporal variability with maximum velocities of about 35 cm s seasonal means as well as currents averaged across the channel are only a few cm s in the surface water a steady southward flow in the middle of the channel indicates the canarycurrent in this area during fall a strong northward current is observed close to the african shelf though the canarycurrent strengthens during summer and fall due to an increase of the trade winds the transport in the channel decreases or turns northward during that time due to the enhanced poleward current at the eastern side a northward undercurrent with a mean velocity of 2 3 cm s is observed at the african slope in 950 m depth the poleward transport of aaiw increases during fall and a strong influence of relatively fresh aaiw is observed during that time most of the observations fit well to the results of the canigo model but the occurrence of mw at the bottom of the channel and the corresponding southward flow cannot be resolved by the model

present day geodynamics of the northern north american cordillera abstract diffuse continental deformation results from interactions at plate boundaries buoyancy forces generated by gradients in gravitational potential energy and loads applied to the base of the lithosphere using finite element models we calculate a deviatoric stress field associated with buoyancy forces and then perform an iterative inversion to calculate deviatoric stress fields associated with boundary forces in the northern north american cordillera our results reveal the presence of two distinct geodynamic domains in the outboard domain approximately equal magnitudes of boundary and buoyancy forces can account for the observed deformation along the aleutian megathrust in contrast large boundary forces related to subduction of the pacific and yakutat slabs dominate the force balance in south central alaska and combine with relatively small buoyancy forces to reproduce the observed kinematic indicators in the inboard domain encompassed by interior and northern alaska and western canada boundary and buoyancy forces alone cannot reproduce the observed deformation therefore we infer that deviatoric stresses due to basal tractions from a deeper mantle convection cell contribute to surface deformation in the inboard domain low effective lithospheric viscosity in south central alaska and the balancing effect of an independent geodynamic system driven by basal tractions in northern alaska combine to confine the anomalously large yakutat related boundary deviatoric stresses to south central alaska deviatoric stresses associated with flat slab subduction of the yakutat microplate are a factor of two greater than boundary force estimates for the andean and indian eurasian convergent margins where buoyancy and boundary forces are roughly equal in magnitude and dominate the force balance

the ichthyoplankton assemblage of the canaries african coastal transition zone a review abstract in this paper we review information on the ichthyoplankton assemblage of the canaries african coastal transition zone c actz this ctz shows the singularity that the canary archipelago interrupts the main flow of the canary current and trade winds introducing large mesoscale variability in the form of island warm wakes and cyclonic and anticyclonic eddies downstream of the islands besides upwelling filaments stretch towards the archipelago from the african coastal upwelling transporting phytoplankton zooplankton and fish larvae they also interact with eddies shed from the islands to exchange water properties and biogenic material all these mesoscale features influence the composition structure abundance and distribution of the larval fish community lfc of the region the canary current cc and eddies shed from the islands drag larvae of island neritic fish species into the oceanic region and contribute along warm wakes to the horizontal distribution of fish larvae upwelling and upwelling filaments transport larvae of african neritic species into the oceanic region these larvae dominate the lfc and account for the relatively high average larval fish abundance found in the c actz during the summer upwelling season filaments originated in the region of cape juby cape bojador are entrained around a quasi permanent cyclonic eddy trapped between gran canaria island and the african coast forming a system through which most of the african neritic larvae may return to the african shelf however some larvae reach the eastern islands of the canary archipelago and they may be spread all over the neritic region of the archipelago by eddies shed from the islands also in summer the distribution of the lfc of the c actz is vertically stratified and fish larvae seem to carry out little or not diel vertical migration overall this study highlights the strong relationship between mesoscale oceanographic processes and the lfc in the c actz

the canary islands coastal transition zone upwelling eddies and filaments 3 pages printed version published in issue aug sep 2004 issue title the canary islands coastal transition zone upwelling eddies and filaments

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

thermochronology in southeast alaska and southwest yukon implications for north american plate response to terrane accretion abstract this study presents the first comprehensive dataset of low temperature thermochronology from 43 bedrock samples collected north of the active yakutat north american plate boundary our apatite and zircon u th he and fission track data reveal the cooling history of the inboard wrangellia composite terrane that is dominated by rapid cooling after late jurassic to early cretaceous arc magmatism followed by very little cooling and exhumation until today deformation resulting in rock exhumation due to the collision of the yakutat microplate is spatially very limited 20 30 km and is concentrated mainly in the chugach prince william terrane and rocks near the border ranges fault focused exhumation from greater depths of ca 10 km with very high rates 5 km myr is localized at the syntaxis region starting ca 10 ma and shifted south through time the rapid exhumation rates are explained by the development of strong feedbacks between tectonically driven surface uplift and erosion which started already before glaciation of the area the shift in the location towards the south is a consequence of continuous readjusting between tectonics and climate which is changing on local and global scales since the late miocene

thermotectonic history of mt logan yukon territory canada implications of multiple episodes of middle to late cenozoic denudation abstract the extreme relief of the st elias mountains including mt logan is suggestive of a young mountain belt new apatite fission track data indicate that the mt logan massif experience rapid low temperature cooling during three distinct periods during the middle eocene middle miocene and pliocene each cooling episode the magnitude of which varies due to temporal variations in recorded paleogeothermal gradients can be tentatively linked to a tectonic cause eocene cooling may be due to re equilibration of isotherms following normal faulting caused by a combination of thermal weakening of the crust and a decrease in regional compressional stress due to the 43 ma change in relative motions between the pacific and north american plates the cause of miocene cooling is problematic and could reflect denudation in response to initial underplating of the yakutat terrane or a recorded change in heat flow unrelated to denudation pliocene cooling reflects erosion due to surface uplift that produced the spectacular present day topography of the st elias mountians this surface uplift is probably related to the coeval significant change in relative motion between the north american and pacific plates and or resistance to subduction by the yakutat terrane

cooling history of the st elias syntaxis southeast alaska revealed by geochronology and thermochronology of cobble sized glacial detritus

mineral chemistry and oxygen isotopic analyses of uraninite pitchblende and uranium alteration minerals from the cigar lake deposit saskatchewan canada abstract the cigar lake unconformity type u deposit is one of the largest and highest grade u deposits in the proterozoic athabasca basin northern saskatchewan canada cigar lake has recently been the focus of an international 3 a collaborative program in which this u deposit was studied as a natural analogue for a spent nuclear fuel repository the deposit is located near the eastern margin of the athabasca basin 430 m below the surface at the intersection between hudsonian age faults and the unconformity between athabasca group sandstones and aphebian metasediments three stages of u mineralization have been identified based on cross cutting relationships and textures observed in thin section and back scattered electron bse images o isotope data and chemical compositions all stages of u mineralization have been variably altered to ca rich u hydrate minerals or uranyl oxide hydrate minerals and coffinite u pb chemical ages of the 3 stages of u mineralization from cigar lake coincide with the 3 major fluid events that precipitated clay and silicate minerals at 1500 ma 950 ma and 300 ma throughout the entire athabasca basin stage 1 and 2 uraninite and pitchblende have the lowest 18o values that range from 30 1 to 15 2 whereas stage 3 uraninite has 18o values ranging from 10 0 to 3 4 uranyl oxide hydrate minerals have 18o values that range from 11 3 to 8 2 whereas uranyl minerals have much higher 18o values based on u pb chemical ages 18o values and petrographic relationships of u alteration minerals associated with primary u mineralization the cigar lake u ore is similar to u ore from other unconformity type u deposits in the athabasca basin therefore the cigar lake ore deposit although surrounded by clay and sandstone barriers has been effected by the same fluid events that have altered other unconformity type u deposits in the athabasca basin the 3 stages of ore formation and associated alteration minerals permit the detailed study of fluids responsible for u deposition and alteration this information provides the necessary context for the evaluation of the cigar lake deposit as a natural analogue for the disposal of spent nuclear fuel in underground vaults in rocks of the canadian shield

apatite u th he thermochronometry using a radiation damage accumulation and annealing model helium diffusion from apatite is a sensitive function of the volume fraction of radiation damage to the crystal a quantity that varies over the lifetime of the apatite using recently published laboratory data we develop and investigate a new kinetic model the radiation damage accumulation and annealing model rdaam that adopts the effective fission track density as a proxy for accumulated radiation damage this proxy incorporates creation of crystal damage proportional to production from u and th decay and the elimination of that damage governed by the kinetics of fission track annealing the rdaam is a version of the helium trapping model hetm shuster d l flowers r m and farley k a 2006 the influence of natural radiation damage on helium diffusion kinetics in apatite earth planet sci lett 249 148 161 calibrated by helium diffusion data in natural and partially annealed apatites the chief limitation of the hetm now addressed by rdaam is its use of he concentration as the radiation damage proxy for circumstances in which radiation damage and he are not accumulated and lost proportionately from the crystal by incorporating the rdaam into the hefty computer program we explore its implications for apatite u th he thermochronometry we show how u th he dates predicted from the model are sensitive to both effective u concentration eu and details of the temperature history the rdaam predicts an effective he closure temperature of 62 c for a 28 ppm eu apatite of 60 m radius that experienced a 10 c ma monotonic cooling rate this is 8 c lower than the 70 c effective closure temperature predicted using commonly assumed durango diffusion kinetics use of the rdaam is most important for accurate interpretation of u th he data for apatite suites that experienced moderate to slow monotonic cooling 1 0 1 c ma prolonged residence in the helium partial retention zone or a duration at temperatures appropriate for radiation damage accumulation followed by reheating and partial helium loss under common circumstances the rdaam predicts u th he dates that are older sometimes much older than corresponding fission track dates nonlinear positive correlations between apatite u th he date and eu in apatites subjected to the same temperature history are a diagnostic signature of the rdaam for many but not all thermal histories observed date eu correlations in four different localities can be explained with the rdaam using geologically reasonable thermal histories consistent with independent fission track datasets the existence of date eu correlations not only supports a radiation damage based kinetic model but can significantly limit the range of acceptable time temperature paths that account for the data in contrast these datasets are inexplicable using the durango diffusion model the rdaam helps reconcile enigmatic data in which apatite u th he dates are older than expected using the durango model when compared with thermal histories based on apatite fission track data or other geological constraints it also has the potential to explain at least some cases in which u th he dates are actually older than the corresponding fission track dates

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

joint modeling of lithosphere and mantle dynamics elucidating lithosphere mantle coupling 1 we provide new insights into the lithosphere mantle coupling problem through a joint modeling of lithosphere dynamics and mantle convection and through comparison of model results with the high resolution velocity gradient tensor model along the earth s plate boundary zones using a laterally variable effective viscosity lithosphere model we compute depth integrated deviatoric stresses associated with both gravitational potential energy gpe differences and deeper mantle density buoyancy driven convection when deviatoric stresses from horizontal basal tractions associated with deeper density buoyancy driven convective circulation of the mantle are added to those from gpe differences the fit between the model deviatoric stress field and the deformation indicators improves dramatically in most areas of continental deformation we find that the stresses induced by the horizontal tractions arising from deep mantle convection contribute approximately 50 of the magnitude of the earth s deviatoric lithospheric stress field we also demonstrate that lithosphere asthenosphere viscosity contrasts and lateral variations within the lithospheric plate boundary zones play an important role in generating the right direction and magnitude of tractions that yield an optimal match between deviatoric stress tensor patterns and the deformation indicators

control of lithospheric inheritance on neotectonic activity in northwestern canada lithospheric inheritance is thought to affect the location and reactivation of tectonic structures through successive cycles of supercontinent formation and dispersal however its relation to neotectonic activity remains unclear in northwestern canada abundant seismicity throughout the northern canadian cordillera ncc is geographically confined by several crustal scale boundaries yet its southern extent terminates abruptly along the inferred westward extension of a late cretaceous rifted margin boundary called the liard transfer zone ltz we use seismic data to show that the uppermost mantle beneath the cordillera exhibits a sharp north south contrast in fabric across the ltz south of the ltz fast axes of seismic wave propagation align closely with the lithospheric mantle fabric orientation of the adjacent canadian shield north of the ltz fast axes are reoriented subparallel to the motion of the pacific plate and follow the strike of the large dextral strike slip tintina and denali faults we attribute changes in anisotropic delay times across the tintina and denali faults to localized shear within the lithosphere this implies that the crust and lithospheric mantle remained mechanically coupled during shearing we propose that the contrast in uppermost mantle structure across the ltz reflects a change in the nature and origin of the lithospheric mantle from inherited rifted margin structures which affects the stability of the lithosphere and limits the extent of seismic activity within the ncc these results indicate that neotectonic activity in modern cordilleras is controlled in part by inherited upper mantle structures

physical and bio optical observations of oceanic cyclones west of the island of hawai i abstract interdisciplinary observations of mesoscale eddies were made to the west of the island of hawai i a central goal of the studies is to improve our understanding of the coupling of physical biological and biogeochemical processes that occur within these eddies a specific objective was to test the hypothesis that the physical mechanisms of mesoscale eddies result in increases in nutrient availability to the euphotic layer increases in primary production changes in biological community compositions and size distributions and increases in carbon flux to the deep sea data were obtained from ships surface drifters and satellite sensors during three separate field experiments variability was associated with two well developed cyclonic cold core mesoscale eddies cyclone noah and cyclone opal which were observed during the e flux i survey november 6 20 2004 and e flux iii survey march 10 27 2005 field campaigns respectively no mesoscale eddies were found during e flux ii survey january 10 19 when winds were erratic in magnitude and direction supporting the hypothesis that persistent trade winds drive the production of cold core mesoscale eddies in the lee of the hawaiian islands cold core eddies were present in the e flux study area for about 2 3 of a year beginning may 1 2004 and trade winds prevailed for about 3 4 of the same year both cyclone noah and cyclone opal were generated during strong persistent northeasterly trade wind conditions and appeared downwind of the alenuihaha channel separating the islands of maui and hawai i the likely production mechanism for both mesoscale cold core eddies involves localized wind stress curl induced upwelling produced by trade wind forcing cyclone noah was likely spun up by strong trade winds just to the southwest of the alenuihaha channel 20 10 n 156 40 w between august 13 and 21 2004 based on modis satellite sea surface temperature sst imagery and quikscat satellite wind data and apparently began to dissipate by mid december 2004 cyclone opal was likely spun up by strong trade winds between february 2 and 18 2005 southwest of the alenuihaha channel 20 30 n 156 30 w but was no longer evident in april 2005 both cyclone noah and cyclone opal had strong physical chemical and biological expressions and displayed similar maximum tangential current speeds of 60 cm s 1 however cyclone opal was more symmetric and larger in scale roughly 180 200 km in diameter compared to 160 km in horizontal scale for cyclone noah both mesoscale eddies displayed significant doming in their centers and in some cases outcroppings of isothermal isopycnal nutrient and chlorophyll a isopleths after formation and a slow drift southward cyclone noah remained in nearly the same location roughly 19 60 n 156 50 w during the 3 week in situ sampling period whereas cyclone opal drifted southward by 165 km over a similar time span of sampling interestingly the physical manifestations of both features were relatively unchanged during the ship based surveys however the biology appears to have evolved within cyclone opal the present report sets the context for several other e flux studies

mesoscale distribution of clupeoid larvae in an upwelling filament trapped by a quasi permanent cyclonic eddy off northwest africa abstract the distribution of fish larvae in relation to a filament shed from the northwest african coastal upwelling was studied in february 2001 during the cruise the filament was located between 27 n and 28 n extending from the african coastal upwelling zone to the south of fuerteventura island canary islands this filament was trapped and remained over the quasi permanent cyclonic eddy observed in previous studies almost all sardina pilchardus engraulis encrasicolus and sardinella aurita larvae caught during the cruise were associated with upwelled waters and filament structures the sampled larval fish assemblage was composed by 12 6 of clupeoid larvae these were distributed as follows 73 9 were s pilchardus 20 7 were e encrasicolus and 5 4 were s aurita their distribution suggested that the coastal upwelling filament is a mechanism of transport from the upwelling area to oceanic waters but its junction with the generated cyclonic eddy may not always work as a retention structure for those transported larvae as described in previous studies physiological studies based on gut fluorescence and ets activity of clupeoid larvae as proxies for grazing and respiration respectively denoted a switch from pigmented food near the upwelling zone to unpigmented food toward the ocean this pattern agrees with observed mesozooplankton feeding along an upwelling filament in previous studies therefore this work confirms the close relationship between clupeoids distribution and mesoscale circulation as well as constitutes the first assessment of the metabolic activity of those larvae in the region

predicting the lithospheric stress field and plate motions by joint modeling of lithosphere and mantle dynamics the way in which basal tractions associated with mantle convection couples with the lithosphere is a fundamental problem in geodynamics a successful lithosphere mantle coupling model for the earth will satisfy observations of plate motions intraplate stresses and the plate boundary zone deformation we solve the depth integrated three dimensional force balance equations in a global finite element model that takes into account effects of both topography and shallow lithosphere structure as well as tractions originating from deeper mantle convection the contribution from topography and lithosphere structure is estimated by calculating gravitational potential energy differences the basal tractions are derived from a fully dynamic flow model with both radial and lateral viscosity variations we simultaneously fit stresses and plate motions in order to delineate a best fit lithosphere mantle coupling model we use both the world stress map and the global strain rate model to constrain the models we find that a strongly coupled model with a stiff lithosphere and 3 4 orders of lateral viscosity variations in the lithosphere are best able to match the observational constraints our predicted deviatoric stresses which are dominated by contribution from mantle tractions range between 20 70 mpa the best fitting coupled models predict strain rates that are consistent with observations that is the intraplate areas are nearly rigid whereas plate boundaries and some other continental deformation zones display high strain rates comparison of mantle tractions and surface velocities indicate that in most areas tractions are driving although in a few regions including western north america tractions are resistive citation ghosh a w e holt and l m wen 2013 predicting the lithospheric stress field and plate motions by joint modeling of lithosphere and mantle dynamics

a modeling study of the coastal eastern boundary current system off iberia and morocco to investigate the northern canary current system nccs results from four numerical experiments of increasing complexity are examined experiment 1 which uses seasonal wind forcing only shows that as expected wind forcing is the key generative mechanism for the current upwelling meander eddy and filament structures experiments 2 and 3 which have the additional effects of irregular coastline geometry show the following capes are areas for enhanced upwelling extensive filaments maximum current velocities and enhanced growth of cyclonic meanders and eddies an embayment like the gulf of cadiz is a primary region for anticyclonic meander and eddy development the results from the complex flow regime of experiment 4 which has the additional effects of thermohaline gradients and mediterranean outflow highlights the major characteristics and unique features such as the generation of meddies of the nccs with relatively close similarities to field observations

the dynamics of plate tectonics and mantle flow from local to global scales plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries but observationally constrained high resolution models of global mantle flow remain a computational challenge we capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions with individual plate margins resolved down to a scale of 1 kilometer back arc extension and slab rollback are emergent consequences of slab descent in the upper mantle cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high viscosity slabs altering the velocity of oceanic plates viscous dissipation within the bending lithosphere at trenches amounts to 5 to 20 of the total dissipation through the entire lithosphere and mantle

lagrangian transport pathways in the northeast atlantic and their environmental impact this study focused on mapping the general transport pathways of the northeast atlantic ocean by using the regional oceanic modeling system to calculate ocean current velocity components u v w and ariane an off line fortran code dedicated to the computation of three dimensional streamlines from velocity fields to calculate the transport of particles around the numerical model domain the study was undertaken using a 10 year climatic simulation statistical comparisons with satellite and in situ data showed that the ocean circulation model captured known regional oceanographic features four depth ranges showed different lagrangian transport pathways 0 10 m 20 200 m 300 500 m and 600 2000 m confirming that these routes are consistent with the known ocean circulation patterns our results were supported by multiple sources i connectivity between the african coast and the canary islands for sardine sardina pilchardus anchovy engraulis encrasicolus ii panmixia of lobsters scyllarides latus and palinurus elephas and european conger eel conger conger iii connectivity between azores and canary archipelagos for sponge phorbas fictitius and iv observed drifting of crude oil from the prestige oil tanker spill these results should help guide future observational campaigns as well as the interpretation of open ocean transport patterns and the distribution of marine organisms and chemical tracers in the northeast atlantic region

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

do submesoscale frontal processes ventilate the oxygen minimum zone off peru the peruvian upwelling system encompasses the most intense and shallowest oxygen minimum zone omz in the ocean this system shows pronounced submesoscale activity like filaments and fronts we carried out glider based observations off peru during austral summer 2013 to investigate whether submesoscale frontal processes ventilate the peruvian omz we present observational evidence for the subduction of highly oxygenated surface water in a submesoscale cold filament the subduction event ventilates the oxycline but does not reach omz core waters in a regional submesoscale permitting model we study the pathways of newly upwelled water about 50 of upwelled virtual floats are subducted below the mixed layer within 5 days emphasizing a hitherto unrecognized importance of subduction for the ventilation of the peruvian oxycline

spatiotemporal evolution of upwelling regime along the western coast of the iberian peninsula 1 the spatial and temporal variability of upwelling regime along the western coast of the iberian peninsula ip has been analyzed by means of two different but complementary databases quikscat satellite database which is available from mid 1999 with a high spatial resolution 0 25 0 25 and pacific fisheries environmental laboratory pfel database with a coarser spatial resolution 1 1 but extending back to 1967 the combined use of both databases allows determination of the spatial variability of ekman transport and pumping and identification of temporal trends in upwelling signal upwelling favorable conditions are observed during spring and summer apart from this well known seasonality on upwelling regime along the western coast of the ip some other features have been identified 1 upwelling occurs simultaneously along the entire western coast of the ip but is undoubtedly more complex closer to particular features of the shoreline 2 positive ekman pumping is more intense near capes sao vicente and rocha during spring summer and near cape finisterre all over the year 3 more favorable upwelling conditions have been observed in february and november during the last decade this result is corroborated by sea level pressure composites which show the existence of abnormally high pressures close to the ip during the last decade compared to the historical records 1948 2006 4 the decadal variability of ui is higher in autumn winter than in spring summer 5 monthly upwelling trends indicate a weakening in upwelling intensity during most of the year with the exception of february june and july

dynamic surface topography a new interpretation based upon mantle flow models derived from seismic tomography the very long wavelength i e in the degree range l 1 8 dynamic topography at the earth s surface estimated by isostatic reduction of the observed topography is shown to be in good agreement with the topography predicted by a model of viscous flow in the mantle this flow model was previously derived by independent consideration of the observed nonhydrostatic geoid and is based upon a recent model of large scale seismic shear velocity heterogeneity in the mantle our estimate and prediction of the long wavelength dynamic surface topography reveals significant depressions 2 3 km of the continental shields relative to their hydrostatic reference positions

palaeocene recent plate boundaries in the ne atlantic and the formation of the jan mayen microcontinent abstract breakup and sea floor spreading between greenland and eurasia established a series of new plate boundaries in the north atlantic region since the late palaeocene a conventional kinematic model from pre breakup to the present day assumes that eurasia and greenland moved apart as a two plate system however new regional geophysical datasets and quantitative kinematic parameters indicate that this system underwent several adjustments since its inception and suggest that additional short lived plate boundaries existed in the ne atlantic among the consequences of numerous plate boundary relocations is the formation of a highly extended or even fragmented jan mayen microcontinent and subsequent deformation of its margins and surrounding regions the major oligocene plate boundary reorganization and microcontinent formation might have been precluded by various ridge propagations and or short lived triple junctions ne and possibly sw of the jan mayen microcontinent from the inception of sea floor spreading 54 ma to c18 40 ma our model implies a series of failed ridges offshore the faeroe islands a northern propagation of the aegir ridge ne of the jan mayen microcontinent and a series of triple junctions and or propagators in the southern greenland basin

the transition zone of the canary current upwelling region abstract like all the major upwelling regions the canary current is characterised by intense mesoscale structure in the transition zone between the cool nutrient rich waters of the coastal upwelling regime and the warmer oligotrophic waters of the open ocean the canary island archipelago which straddles the transition introduces a second source of variability by perturbing the general southwestward flow of both ocean currents and trade winds the combined effects of the flow disturbance and the eddying and meandering of the boundary between upwelled and oceanic waters produce a complex pattern of regional variability on the basis of historical data and a series of interdisciplinary field studies the principal features of the region are described these include a prominent upwelling filament originating near 28 n off the african coast cyclonic and anti cyclonic eddies downstream of the archipelago and warm wake regions protected from the trade winds by the high volcanic peaks of the islands the filament is shown to be a recurrent feature apparently arising from the interaction of a topographically trapped cyclonic eddy with the outer edge of the coastal upwelling zone its role in the transport and exchange of biogenic material including fish larvae is considered strong cyclonic eddies observed throughout the year drift slowly southwestward from gran canaria one sampled in late summer was characterised by large vertical isopycnal displacements apparent surface divergence and strong upwelling producing a fourfold increase in chlorophyll concentrations over background values such intense eddies can be responsible for a major contribution to the vertical flux of nitrogen the lee region of gran canaria is shown to be a location of strong pycnocline deformation resulting from ekman pumping on the wind shear boundaries which may contribute to the eddy formation process

statistical trends in the intraplate stress field the world stress map wsm database contains thousands of intraplate stress indicators with the potential to provide important constraint for arguments about the relationship between tectonic stresses and both the kinematics and dynamics of plate motion previous studies which relied almost exclusively on visual inspection of the data established the existence of broad regions of uniform maximum horizontal compressive stress orientation shmax and stress regimes on a regional scale in the present study we present a statistical analysis of the wsm stress indicators with the aim of quantifying trends in both the shmax orientations and stress regimes the analysis was carried out within 5 5 bins which provide a resolution of several hundred kilometers only the 4537 high quality wsm indicators with rating of a to c were used in the analysis we present results for two types of analysis on the information contained within the bins first we evaluate the spatial distribution of the average stress regime normal strike slip or thrust second we apply the rayleigh test a standard statistical method in the analysis of directional data to the distribution of shmax orientations to test the null hypothesis that the orientations are random an important aspect of our study is the quantification of the conclusions drawn from visual inspection of the world stress map our results indicate that broad regions of uniform shmax orientations exist in most continental regions at high confidence levels 90 and 95 and are less robust in the slowest moving continental plates we also quantify the predominance of strike slip and compressional stress regimes in continental regions importantly our analysis provides information about trends in the shmax orientations in regions where large amounts of scatter in the directional data prevented conclusions being drawn from visual inspection of the data for example in western north america and continental australia furthermore we find a strong correlation between average shmax orientations and both the ridge push torque and the absolute plate velocity azimuths our observation that a greater number of shmax orientations correlate with the ridge push torque directions is further evidence that the intraplate stress field is strongly influenced by the ridge push force

lee region of gran canaria the mountainous canary islancls present obstacles to the trade wincls ancl to the canary current flowing equatorwarc past them in situ observations of hydrographic properties ancl surface wincls south of gran canaria together with advancecl very high resolution racliometer ancl synthetic aperture racial images e uring 2 weeks in summer 1995 are analyzecl a cyclonic edcly shecl l rom the west of the islancl c1riftecl southwestwarcl at 5 s j while the southeast coast was approachecl by an upwelling filament originating off nw africa a wincllee region bounclecl by intense horizontal shear lines hacl a weak return islandwarcl wincl in its center the lee formee a triangulai c1iurnally varying war111 water 001 with two sea surface temperature maxima separatecl by lower temperatures below the return wincl shallow temperature stratification occurrecl behincl the islancl in contrast to the l1niform surface mixecllayer in exposecl regions upwelling ancl clownwelling of 10 20 111 were indicatecl on the cyclonic ancl anticyclonic sicles of the lee region in the sar la u lines of strong current shear along a temperature front between the cyclonic eclcly the upwelling filament were iclentifiable i iowever the racial images were clominatecl atmospheric phenomena including mountain lee wave paclcets winclrows and wincl lines estimation of the wincl field l rom the sar backscatter intensity revealed ex structure and intensification on the eclges of the warm lee

the structure of mountain fronts commonly the part of a mountain front which is visible at the surface consists of foreland dipping thrust belt rocks elevated above their regional structural position and overlain more or less conformably by molasse several explanations for their geometry are possible 1 major detachments exist within or beneath the molasse resulting in transport of the foreland basin examples of this geometry come from the swiss molasse plain the southern pyrenees and the mackenzie mountains of canada 2 displacement is lost on major backthrusts beneath the frontal monocline examples cited here are the rockies of alberta the sulaiman ranges of pakistan the mackenzies and the andes in peru 3 thrust sheets travelled over an old land surface and syntectonic molasse contemporaneously offlaps the topographic high of the thrust front this phenomenon occurs along the alpine thrust front in haute provence 4 the frontal fold represents deformation above a large scale thrust tip no unequivocal example of tip line strain at this scale has been recorded although this type of deformation may occur in the brooks range of alaska in many areas mountain fronts show a combination of these idealized geometries

the influence of mesoscale physical processes on the larval fish community in the canaries ctz in summer abstract we have studied the relation between the hydrography the composition and horizontal structure of the larval fish community and the horizontal distribution patterns of larval fish abundances in an area characterised by strong mesoscale oceanographic activity located between the canary islands and the african coast the canaries coastal transition zone during august 1999 upwelling upwelling filaments cyclonic and anticyclonic eddies and island wakes are typical mesoscale features of the northwest african coast in summer a single upwelling filament off cabo juby was joined in mid august by a second that originated about 100 km to the north the two filaments flowed together and merged 100 km offshore the merged filament was partially entrained around a cyclonic eddy trapped between the canary islands and the african coast and interacted with cyclonic and anticyclonic eddies shed from gran canaria mesoscale oceanographic features strongly influenced the horizontal distributions of fish larvae eddies acted as a mechanism of concentration while upwelling filaments were dispersive transporting larvae from the african neritic zone into oceanic areas and towards the canary archipelago this transport was the major cause of the predominance of neritic larvae in the composition of the larval fish community of the area the results also suggest 1 that anchovy larvae are good indicators of the offshore displacement of upwelled water 2 that the alternation between anchovy and sardine as species dominant in the larval fish community of the area during summer depends upon the water temperature in the african upwelling region anchovy dominating at higher temperature 3 that a coupling of anchovy and sardine spawning with the mesoscale oceanographic structure formed by the upwelling filaments and trapped eddy overcomes the negative effect that ekman transport has on their populations

a revised crustal stress orientation database for canada abstract the canadian database on contemporary crustal stress has not been revised systematically in the past two decades here we present the results of our new compilation that contains 514 new data records for the orientation data of maximum compressive horizontal stress and 188 data records that were re assessed in total the canadian stress database has now 1667 data records which is an increase of about 45 from these data a new canadian stress map as well as one for the province of alberta is presented to analyse the stress pattern we use the quasi median on the circle as a smoothing algorithm that generates a smoothed stress map of the maximum compressive horizontal stress orientation on a regular grid the newly introduced quasi interquartile range on the circle estimates the spreading of the data and is used as a measure for the wave length of the stress pattern the result of the hybrid wavelength analysis confirms that long spatial wavelength stress patterns 1000 km exist in large areas in canada the observed stress pattern is transmitted through the intra plate regions the results reveal that shorter spatial wave length variation of the maximum compressive horizontal stress orientation of less than 200 km prevails particularly in south eastern and western canada regional stress sources such as density contrasts active fault systems crustal structures etc might have a significant impact in these regions in contrast to these variations the observed stress pattern in the alberta basin is very homogeneous and mainly controlled by plate boundary forces and body forces the influence of curvature of the rocky mountains salient in southern alberta is minimal the present day horizontal stress orientations determined herein have important implications for the production of hydrocarbons and geothermal energy in the alberta basin

unusual mantle poisson s ratio subduction and crustal structure in central alaska 1 subduction zones alter the upper plate in a variety of ways including metasomatism via slab derived fluids and accretion of exotic terranes these processes should produce distinctive seismic signatures as seismic velocities are sensitive to compositional variations a new method is developed to estimates depths to interfaces and poisson s ratio vp vs ratio for dipping layered structures by stacking teleseismic receiver functions it also estimates crustal vp vs and thickness using this method we analyze a broadband data set from the central alaska subduction zone to seek evidence for mantle wedge composition crustal thickness varies from 27 to 45 km and crustal vp vs indicates an intermediate to mafic composition expected for these accreted island arc terranes inversions for mantle structure confirm the presence of a 15 20 km thick low velocity zone atop of the downgoing plate to 130 km depth perhaps subducted crust of an exotic terrane vp vs in the mantle wedge allows for 15 15 serpentinization where the slab is 80 km deep and the wedge is cold where the slab is deeper vp vs for the mantle wedge is unusually low 1 7 this value is lower than predicted for any common mantle mineral and may indicate significant quantities of quartz provided that past physical properties measurements are not grossly in error these results suggest that the mantle wedge in subduction zones can occasionally differ substantially in bulk composition from normal subcrustal mantle perhaps because collisions of exotic terranes cause tectonic mixing of crustal material into the mantle

uranium series radionuclide and element migration around the sanerliu granite hosted uranium deposit in southern china as a natural analogue for high level radwaste repositories abstract the sanerliu uranium deposit located in hunan province south china has a number of features analogous to aspects considered in the performance assessment of concepts for the disposal of high level radwaste deep in granite the deposit is hosted by medium to coarse grained porphyritic granite with a rb sr isochron age of 215 2 6 3 ma the orebodies have a burial depth of more than 160 400 m under the surface of the ground the major uranium mineralizations have u pb ages pitchblende of 103 2 0 6 88 3 0 5 and 51 2 0 4 ma and a hydrothermal origin the isotopic data show that the rb sr systems in the whole rock samples of less and un fractured host granite around the orebodies have been little disturbed since the altered granite formed 132 ma ago such samples have close to secular equilibrium activity ratios for 234 u 238 u 230 th 234 u and 226 ra 230 th indicating that obvious water rock interactions have not taken place in them within the interval of at least the last 1 ma the migration of uranium thorium and most trace elements in the ores and the host granite are limited often less than 30 35 m over 51 ma the alpha activity ratios 234 u 238 u 230 th 234 u and 226 ra 230 th for the samples from the fracture zones show obvious deviations from secular equilibrium indicating the deposition of uranium during the last 1 ma and of radium during the last 10 3 yr the fracture zones are channels for groundwater flow however the migration of uranium series radionuclides along the fracture zones is limited by adsorption onto the clays this is confirmed by the absence of any hydrogeochemical indication on the ground surface of the orebodies the ores have been well preserved in a natural aquifer system without any specially designed artificial barriers the migration behavior of radionuclides in the ores of the sanerliu deposit may be termed a worse case scenario for the safety assessment of a high level radwaste disposal repository hosted by granitic rocks

sandstone hosted uranium deposits in northern saskatchewan as natural analogs to nuclear fuel waste disposal vaults abstract proterozoic u deposits have been preserved in sandstone formations on several precambrian shields and give testimony to the compositions and conditions required for the safe disposal of nuclear fuel wastes the unconformity type u deposits in the athabasca basin of northern saskatchewan are discussed here in detail conditions for ore formation in the saskatchewan deposits were similar to those expected around a waste package in terms of pressure temperature and salinity of the solutions secondary dispersion of u and other elements of interest resulting from groundwater interactions is very limited only radiogenic pb appears to have been dispersed to any extent two processes involved in the ore formation have a direct bearing on the stability of fuel waste and of buffer and backfill in the nearfield these are redox control of groundwater by methane and quartz dissolution with the former process still active

differential distribution of diatoms and dinoflagellates in a cyclonic eddy confined in the bay of la paz gulf of california the differential distribution of diatoms and dinoflagellates in the bay of la paz gulf of california mexico was analyzed in summer of 2009 when a cyclonic eddy confined in the bay dominated the circulation an uplift of the nutricline in the eddy drove high concentrations of nutrients to the euphotic layer a differential phytoplankton distribution was observed to be associated with the eddy there was an abundance of dinoflagellates close to the center of the cyclonic eddy whereas diatoms were more abundant at the periphery a significant inverse correlation r 0 62 p 0 002 was found between the temperature at 25 m depth and the dinoflagellates abundance based on the temporal evolution of chlorophyll measured by modis satellite images and a conceptual model proposed for the lifecycle of eddies the cyclonic eddy may have been an old decaying structure the effect of the cyclonic eddy on the phytoplankton distribution in this small semienclosed region was apparently similar to that found in larger eddies in the open ocean but this is the first time such a differential distribution has been found associated to a confined eddy

graphite ch4 h2o co2 equilibria at low grade metamorphic conditions equilibrium calculations and published phase equilibria are used to show that at temperatures below 400 c and pressures above 300 bar the fluids coexisting with graphite in the c o h system consist either of co2 h2o mixtures or ch4 h2o mixtures bulk fluid compositions consisting of ch4 h2o will unmix to methane rich fluid and h2o rich liquid at temperatures below about 325 c compositions on the co2 h2o join will unmix only at temperatures below about 275 c oxygen fugacity in the ch4 h2o graphite three phase region is fixed at constant p and t and approximately equal to that of the quartz magnetite fayalite assemblage in the co2 h2o graphite three phase region oxygen fugacity is about three orders of magnitude greater from the end stages of diagenesis to temperatures of 300 c and possibly 400 c in salt rich systems many metamorphic rocks may contain ch4 h2o fluids rather than co2 h2o mixtures thus metamorphic reactions involving carbonate minerals would involve ch4 graphite and h2o rather than co2 the immiscibility between ch4 and h2o could result in the common occurrence of methane natural gas in low grade metamorphic terrains

the influence of natural radiation damage on helium diffusion kinetics in apatite abstract stepwise degassing diffusion experiments on 39 different apatite samples using radiogenic 4he and proton induced 3he reveal a range in closure temperature tc from 50 to 115 c for a cooling rate of 10 c myr there is no correlation between helium diffusion and apatite chemistry including f cl ratio but the closure temperature is positively correlated with the radiogenic 4he concentration 4he in each sample we argue that 4he is a proxy for a sample s natural exposure to actinide radioactivity below the closure temperature and that helium diffusion in apatite is impeded by radiation induced damage to the apatite structure the kinetics must therefore be an evolving function of time measured diffusivities thus reflect a snapshot in time and cannot alone be applied to the thermochronometric interpretation of a given sample the effect of radiation damage on helium diffusion appears to far exceed other known controls on helium diffusivity including grain size our diffusion data are well described by a previously proposed quantitative model that consists of two arrhenius relations one for volume diffusion through undamaged mineral structure and one for release of helium from radiation damage traps the unknown parameters in this trapping model were determined from the diffusion experiments and allow us to develop a tentative mathematical function that relates diffusivity to temperature and 4he by inserting this function into a 4he production diffusion model we have explored how these results affect the interpretation of apatite u th he thermochronometry the model predicts that the effective 4he closure temperature of apatite will vary with cooling rate and effective u concentration eu and may differ from the commonly assumed tc of 70 c by up to 15 c the 4he partial retention zone will look similar to previous expectations but its depth will depend on accumulation time and on eu most notably samples subjected to reheating after accumulation of substantial radiation damage will be more retentive than previously expected these predictions are consistent with recent observations of unexpected apatite u th he ages in some settings

late cenozoic tectonic activity and its significance in the northern junggar basin northwestern china abstract the dingshan area located in the northern part of the junggar basin of northwestern china is a significant prospect area for sandstone type uranium deposits in china where mainly cenozoic rocks were deposited the cenozoic strata can be divided into four units according to the prior data and our own field observation sedimentary studies indicate that most cenozoic strata were deposited under a hot and arid climate in a continental environment the sedimentary facies are alluvial fan meandering fluvial and fluvio lacustrine field investigation and interpretation of satellite images suggest that cenozoic tectonics in the area is characterized by reactivation of early deep seated thrusts resulting in extensional fractures and formation of many small depressions in the shallow crustal level measurement of joint orientations suggests that regional shortening direction trends in north south in the middle pleistocene as indicated by the esr electronic spin resonance age of 0 1 0 4 ma obtained from fault gouge and gypsum deposits a four stage sedimentation tectonic evolution model of the northern junggar basin during the late cenozoic can be established based on reconstruction of sedimentary filling processes and cenozoic tectonic movements we suggest that landform evolution and groundwater movement are controlled by active tectonics indicating that late cenozoic tectonic activities may also play important roles in the formation of sandstone type uranium deposits therefore a new metallogenic model for sandstone type uranium deposits is proposed

on the relationships between slab dip back arc stress upper plate absolute motion and crustal nature in subduction zones 1 statistical analysis of modern oceanic subduction zone parameters such as the age of a downgoing plate or the absolute plate motions is performed in order to investigate which parameter controls the dip of a slab and conversely what the influence of slab geometry is on upper plate behavior for that purpose parameters have been determined from global databases along 159 transects from all subduction zones that are not perturbed by nearby collision or ridge plateau seamount subduction on the basis of tomographic images slabs that penetrate through or lie on the 670 km discontinuity are also identified the results of the statistical analysis are as follows 1 back arc stress correlates with slab dip i e back arc spreading is observed for deep dips deeper than 125 km larger than 50 whereas back arc shortening occurs only for deep dips less than 30 2 slab dip correlates with absolute motion of the overriding plate the correlation is even better when the slab lies on or even more penetrates through the 670 km discontinuity 3 slabs dip more steeply by about 20 on average beneath oceanic overriding plates than beneath continental ones 4 slabs dip more steeply on average by about 10 near edges 5 slab dip does not correlate with the magnitude of slab pull the age of subducting lithosphere at the trench the thermal regime of the subducting lithosphere the convergence rate or the subduction polarity east versus west the present study provides evidence that the upper plate absolute motion plays an important role on slab dip as well as on upper plate strain retreating overriding plates are often oceanic ones and thus may partially explain the steeper slab dips beneath oceanic upper plates one can infer that low slab dips correlate well with compression in continental advancing upper plates whereas steep dips are often associated with extension in oceanic retreating upper plates excess weight of old slabs is often counterbalanced by other forces probably asthenospheric in origin such as lateral mantle flow near slab edges or anchor forces to determine slab dip

temporal variability of mass transport in the canary current abstract the variability of the canary current is investigated using bimonthly expandable bathythermograph sections from gran canaria island to the african coast between november 1996 and september 1998 the geostrophic transport of the easternmost branch of the canary current is estimated by integrating the thermal wind equation using the layer of neutral density 27 3 roughly 600 m depth as the layer of no motion the yearly average geostrophic transport of this branch of the canary current is 1 8 1 4 10 9 kg s 1 southward approximately half of the transport flows through the channel between the islands of gran canaria and fuerteventura and the other half through the channel between fuerteventura and the african coast the total southward geostrophic transport shows significant seasonal variability ranging from 1 2 0 3 10 9 kg s 1 in may to 2 6 0 1 10 9 kg s 1 in january although november is the only month with considerable differences in geostrophic transport between 1996 and 1997 there is seasonal northward transport in both channels during may in the gran canaria fuerteventura channel and during november in the fuerteventura african coast channel this seasonal pattern is probably linked to autumn weakening of upwelling in the canary islands area and the offshore diversion of this flow at cape ghir

geostrophic and ageostrophic circulation of a shallow anticyclonic eddy off cape bojador a shallow mesoscale anticyclonic eddy observed south of the canary islands with satellite altimetry has been intensively studied with multiparametric sampling hydrographic data from a ctd installed on an undulating nu shuttle platform reveal the presence of a mesoscale anticyclonic eddy of 125 km diameter the difference in sea level anomaly sla between the interior and the edge of the eddy as determined from altimetry is 15 cm which compares well with the maximum dynamic height differences as inferred using a very shallow reference level 130 m further the associated surface geostrophic velocities of about 35 cm s 1 in the northeast and southwest edges of the eddy are in good agreement with direct velocity measurements from the ship deep rosette ctd casts confirm that the structure is a shallow eddy extending no deeper than 250 m before the fusion with another anticyclone the sla tendency temporal rate of change of sea surface height indicates a clear northwestward migration during the two first weeks of november 2008 applying an eddy ssh based tracker the eddy s velocity propagation is estimated as 4 km d 1 use of the qg omega equation diagnoses maximum downward upward velocities of about 2 m d 1 the instability of the canary coastal jet appears to be the mechanism responsible for the generation of the shallow anticyclonic eddy

seasonal to interannual variability in density around the canary islands and their influence on the atlantic meridional overturning circulation at 26 n the meridional interior flow obtained from the rapid array is determined by horizontal density fluctuations at the eastern and western boundary of 26 n the physical causes of these density variations are responsible for fluctuations in the atlantic meridional overturning circulation amoc and through it the meridional heat transport of the atlantic in this modelling study a high resolution ocean model is used to investigate the source and origin of the amoc variability associated with the density fluctuations at the eastern boundary the amoc in the model is in good agreement with the rapid observations and appears to adequately represent the smaller scale features of variability around the canary islands in this paper we identify a robust relationship between the density structure south of the canary islands the local wind stress curl wsc around these islands and the amoc using an empirical orthogonal functions analysis wavelet transform and wavelet coherence we find that the deep density fluctuations at the eastern boundary of 26 n arise from the pumping effect of the spatial pattern of wsc south of the islands these deep density fluctuations drive the amoc both on seasonal and interannual timescales through their influence on the basinwide tilt of the thermocline at seasonal timescales the density fluctuations south of the islands are driven by the wsc and directly influence the amoc at interannual timescales a significant coherence is found between the density fluctuation and the southward umo transport although the origin of these density fluctuations is not explained by the the direct pumping caused by the wsc

distribution and transport of organic matter along a filament eddy system in the canaries nw africa coastal transition zone region abstract the distribution and transport of chlorophyll a chla particulate poc and dissolved doc organic carbon and the respiratory ets activity of the microplankton community were studied along a filament eddy system located in the transition zone between the nw africa upwelling and canary islands waters two independent filaments f1 and f2 stemming from the coastal jet between cape juby and cape bojador merged about 100 km offshore turning southward and onshore forced by the circulation of a recurrent oceanic cyclonic eddy in general the coastal upwelling waters presented higher chla but lower poc doc and ets activity than filament waters however differences in organic carbon distribution and respiratory activity were observed among stations from the two filaments the bio chemical fields were strongly influenced by a complex sub mesoscale hydrography resulting from the interaction of cyclonic and anticyclonic island eddies with the filaments the combined f1 f2 filament system transported 97 1 kg s 1 of excess non refractory total organic carbon e toc a value comparable to other published estimates from upwelling filaments in the ne atlantic about 90 of e toc was exported as doc since eddy re circulation precluded the offshore transport of poc assuming that the calculated transport of e toc is representative of the annual average the yearly offshore transport 3 1 x 109 kg c would represent about 25 of the upwelling primary production of the region of study